Properties of AlFeNiCrCoTi0.5 High-Entropy Alloy Particle-Reinforced 6061Al Composites Prepared by Extrusion

Abstract

(AlFeNiCrCoTi0.5)p/6061Al matrix composites were prepared by cold isostatic pressing combined with equal-diameter angular extrusion. The microstructure and properties of the extruded materials after adding high-entropy alloys were studied. The FCC + BCC dual-phase high-entropy alloy particles mechanically alloyed for 90 h were added to the aluminum matrix, while the composite material formed a diffusion interface after equal-diameter angular extrusion. Compared with the 6061Al matrix, when the content of AlFeNiCrCoTi0.5 was 10%, by two passes, the hardness increased from 52.5 HV to 70.3 HV, the tensile strength increased from 158 MPa to 188 MPa, and the elongation changed from 14.9% to 14.1%. The material had good comprehensive mechanical properties.

1. Introduction

By distributing the alloy particles into the matrix through the process, the comprehensive mechanical properties of the composite could be improved [1]. Particle-reinforced aluminum matrix composites are widely used in production and life. The 6061Al materials change the overall orientation of the material by introducing different reinforcements, which have an important application and development value in aerospace, automobile, aircraft or gear bearings, brake pads, and other fields [2]. High-entropy alloys (HEAs) were proposed by Ye Junwei et al. [3] in 1995, emphasizing the formation of simple solid solution phases by various alloying elements under high mixing entropy [4]. The four major effects of high-entropy alloys [5] were the main reasons for them being added as reinforcing phases to optimize the properties of composites: (1) High entropy effect. A larger entropy value reduces the free energy of the system, inhibits the formation of compounds by various metal constituent elements, and promotes the formation of FCC and BCC simple solid solutions [6]. (2) Lattice distortion effect. HEAs consist of many types of constituent elements and large differences in atomic size. In addition, HEAs have different lattice strains and stresses. These reasons lead to lattice distortion and material strengthening [7]. (3) Hysteresis diffusion effect. The first one is the unique atomic bonding force of each element of HEAs. After the atomic bonding is placed, the energy of the internal system of the alloy decreases to slow down the diffusion of elements, while the slow diffusion inhibits the phenomenon of coarse grains and the generation of fine precipitates, making the material more stable [8]. (4) “Cocktail” effect. Ranganathan [9] proposed that HEAs composed of multiple elements constitute single-phase or multi-phase elements through design and technology and, by changing the main element coordination, can achieve different properties. The overall performance of HEAs is the result of the combined action of each element and each phase structure.

Yu et al. [10] sintered Al0.3CoCrFeNi particle-reinforced copper base material (CMC) after multiple ball milling alloying. A coating transition layer of Cu element was formed around the HEAs, and about 5 μm was formed between the matrix and the HEAs. This transition layer of clean “channels” promotes diffusion between elements, leading to solid solution strengthening to increase the hardness and strength of the material. M. Vaidya et al. [11] conducted a systematic study on the preparation of HEAs by mechanical alloying. Mechanical alloying (MA) and sintering techniques had unique advantages in improving the solid solution and uniform forming of HEAs. The preparation of various HEAs by mechanical alloying was also systematically summarized. The results showed that MA can regulate the phase evolution, thermal stability, and comprehensive properties of the materials. When the CoCrFeNi high-entropy alloy with an equimolar ratio was strengthened by thermochemical processing, it was found that the Al element promoted the formation of nano-γ’phase. The alloy was further strengthened mainly by dislocation strengthening and multi-scale precipitation strengthening. The overall performance of the material after mechanical processing was good. It had a good combination of strength and plasticity, but the plasticity of the material decreased significantly with the increase in Al content [12]. When AlCrFeNi-reinforced 6063Al was prepared by powder metallurgy, HEA powder was evenly distributed after hot extrusion. The interfacial bonding strength of the composites was excellent, while the tensile properties of the composites were improved [13]. Li et al. [14] prepared FeCoNi1.5CrCu/Al matrix composites by mechanical alloying and microwave sintering. HEA particles were closely combined with Al, and the internal reinforcing particles were evenly distributed. After sintering at 480 °C, the material had excellent properties, such as plasticity, toughness, hardness, and strength. During the preparation of Al0.25Cu0.75FeNiCo HEAs particles to strengthen 7075Al, as the volume fraction of HEAs increased, the tensile strength and elongation of the material decreased. Mainly because the reinforcing particles were easy to agglomerate, pores and bubbles appeared between the two phases [15].

In this paper, 6061Al material was enhanced by mechanical alloying AlFeNiCrCoTi0.5 high-entropy alloy powder for 90 h. It was found that, when the high-entropy alloy content was 10% and the extrusion pass was 2, the composite material prepared by extrusion formed a good interface, and the internal pores of the material decreased and became smaller. The purpose was to change the alloying parameters to cause extenuation of the HEA particles, and to achieve a good combination between the reinforcing phase and the matrix during the preparation process. In addition, the balance of properties was achieved by cold isostatic pressing and hot extrusion. Finally, a certain number of extrusions could cause the internal reinforcing phase of the material to be evenly distributed and the structure clearly refined, which could improve the strength and ensure plasticity.

2. Experimental

High-entropy alloys were prepared from Al, Fe, Ni, Cr, Co, and Ti metal powders (8.4 μm) with a purity of 99.99%, produced by Xingrongyuan Technology Co., LTD, Beijing Municipality, China. Each metal particle powder was mixed in a V-shaped dry powder mixer for 10 h to cause it to be evenly distributed. Then, HEAs were prepared by mechanical alloying with a planetary ball mill (QM-3SP2, from Chishun Technology Development Co., Ltd., Nanjing, China). When the HEA particles were put into the planetary ball mill for alloying, the addition of n-heptane reduced cold welding. Argon was used to prevent oxidation and the alloying was shut down for 2 h every 20 h. The grinding was performed at a ball mill speed of 300 r/min for 30 min, 10 h, 20 h, 30 h, 50 h, 70 h, and 90 h, respectively. The density of the high-entropy alloy AlFeNiCrCoTi0.5 is 6.884 g/cm³.

Table 1. The characteristic parameters of each element in high-entropy alloy.

Elements	Al	Fe	Ni	Cr	Co	Ti
Atomic number	13	26	28	24	27	22
Density (g/cm3)	2.7	7.9	8.9	7.19	8.9	4.54
Melting point (°C)	660	1538	1455	1857	1495	1660
Crystal structure	FCC	BCC	FCC	BCC	HCP	HCP
Atomic radius (nm)	1.43	1.26	1.25	1.30	1.25	1.47
Relative atomic mass	26.98	55.84	58.69	58.93	52	47.87
Valence electron concentration	3	8	10	6	9	4
Electronegativity	1.61	1.8	1.91	1.66	1.88	1.54

shows the parameters of each component element of HEAs, and

Table 2. High-entropy alloy system parameters.

HEAs	ΔSmix/[J/(k·mol)]	ΔHmix/(kJ/mol)	δ/%	VEC	χ/%	Tm/K	Ω
AlFeNiCrCoTi0.5	14.70	−17.92	6.24	6.91	13.12	1434	1.40

HEA powder and 6061Al powder (8.4 μm) were mixed in a V-shaped dry powder mixer (ball/material ratio 10:1) for 10 h. AlFeNiCrCoTi0.5/6061Al powders with an HEA content of 5 vol.%, 10 vol.%, and 15 vol.% were prepared by grouping. The specific composition of the 6061Al powder is shown in Table 3.

shows the system parameters of HEAs.

The compound powder was packed into an LDJ200/600–300 cold (Sichuan Aviation Industry Sichuan West Machinery Co., Ltd., Ya’an, China) isostatic pressing mold under argon protection and compacted. The pressure was 275 MPa and the pressure holding time was 300 s, while the pressure rise rate was 30 MPa/s and the pressure reduction rate was 10 MPa/s. After grinding, composite powder samples were hot extruded by the YJ32-315A (Jiangdong Machinery Co., Ltd., Chongqing, China) vertical four-column hydraulic press and self-made equal-diameter angular extrusion mold. The pressure was 25 MPa and the temperature was 450 °C. The material was extruded after heat preservation.

The surface of the material was selected using 800.1000.2000.3000 mesh sandpaper for initial grinding. Then, the MP-2B polishing machine was used for polishing under a diamond polishing agent until the surface of the sample after polishing was smooth. The Bruker AXS D8A X-ray diffractometer (Cu target, 60.0 kV, 80.0 mA, Hangzhou, China) was used for the phase structure of the material analysis. The test angle was 20°~90°, while the scanning speed was 10°/min. Microstructure analysis was carried out by SEM (FEI Verios 460 type, Lianyungang, China) and TEM (Talos L120C, Xi’an, China), and the distribution of interface elements was observed by EDS. The material hardness test was performed by the HV-30 Vickers Hardness Tester (Lianyungang, China) with a load of 3.6 N and a loading time of 15 s. Tensile specimens were prepared by wire cutting and tested at a tensile rate of 3 mm/min with a UTM5305 electronic universal testing machine (Lianyungang, China). The tensile strength and elongation of the materials were analyzed. The fracture morphology of the materials was analyzed by SEM. Figure 1 is a simple schematic diagram of the experimental procedure.

3. Results and Discussion

3.1. HEA Particle Analysis

As the mechanical alloying time increases, Figure 2 shows the detection of AlFeNiCrCoTi0.5 powder by XRD with different ball milling times. Using Jade software and PDF card comparison, the diffraction peaks of each constituent element gradually decreased until they disappeared. Al, Fe, Ni, Cr, Co, and Ti diffractions in the XRD pattern were obvious at 30 min. After alloying for 10 h, the XRD pattern showed that the diffraction peak of Al-element disappeared as a result of alloying. After 30 h of ball milling, the diffraction peak of Co-element gradually disappeared as a result of alloying. In the process of ball milling alloying, the powders of different elements were repeatedly squeezed and collided by the grinding ball. The particles were deformed, fractured, welded, and interdiffused between atoms for in situ self-reaction. A high-entropy alloy reinforced phase was finally formed.

Alloying elements with a high melting point would extend the alloying time and increase the difficulty of alloying. Al with a lower melting point changed first, and elements with a high melting point such as Cr and Ti still had diffraction peaks after Al alloying [16,17].

With the increase in mechanical alloying time, the extruded HEA particles were cold-welded and work-hardened. At the same time, with plastic deformation, stress concentration, lattice fracture, and lattice distortion were intensified, which all strengthen the solid solution phenomenon. If the ball milling time was 70 h, the diffraction peaks of BCC and FCC structures appeared. At this time, AlFeNiCrCoTi0.5 was alloyed to form a dual-phase solid solution structure of FCC + BCC. If the ball milling time was 90 h, the diffraction peaks appeared to broaden while the peak intensity decreased. At this time, the lattice distortion of the material intensified and the dislocations were superimposed, while the grain size decreased.

Scanning electron microscope analysis of AlFeNiCrCoTi0.5 particles with different ball milling time was performed to observe their microstructure and particle size distribution. Figure 3a shows the powder morphology after ball milling for 30 min. Combined with XRD, it can be seen that the powder was not alloyed at this time. Part of the powder was flattened in a short time and had an irregular shape with a particle size of about 11 μm. After ball milling for 10 h, combined with XRD, the material began to be alloyed and formed 520 μm flat particles. At this time, HEA particles were continuously extruded by the impact grinding ball to produce large plastic deformation and cold welding, resulting in an increased particle volume. After 10 h to 20 h of ball milling, the particle size decreased as a result of crushing, and from 20 h to 70 h, the particle size increased as a result of extrusion weld. Figure 3f shows that HEA particles agglomerated after ball milling for 70 h. Combined with XRD analysis in Figure 2, it can be seen that an FCC + BCC dual-phase structure (130 μm) was formed in the completely alloyed material after 70 h. Severe agglomeration should not be used as a reinforcer. If the ball milling was 90 h or 120 h, the particles became smaller (10 μm). The powder morphology and particle size would not change significantly with time. HEA particles tended to deform during ball milling owing to repeated deformation–cold welding–fracturing–cold welding-fracturing [18,19]. Zhou et al. [20] also found that, when CoCrFeNiTiCuMoxVx was prepared by ball milling, the powder particles were small and uniformly distributed (100~200 nm), but it was easy to form sheet-like agglomeration.

Through experiments, it was found that, with the extension of alloying time, the Al element first began to alloy and promoted the formation of the BCC phase of AlFeNiCrCoTi0.5. The diffraction peaks of Cr, Ti, and other alloyed elements disappeared when the time was extended. Finally, after 90 h ball milling, HEAs formed in the FCC + BCC two-phase structure. During mechanical alloying, HEAs were deformed by ball milling and the particle shape was irregular. Over time, the surface energy of the particles was increased by impact and crushing. The particles were extruded and then re-pulverized by cold welding. After 90 h of alloying, the particles not only avoided the agglomeration formed by 70 h ball milling, but also avoided the coarse particles formed by extrusion and cold welding after 120 h ball milling. In the case of small particles, alloyed HEAs should be evenly distributed to avoid agglomeration and ensure the enhancement effect. Therefore, the ball milling time of 90 h was the most optimal.

3.2. Composite Material Analysis

Analyzing and comparing PDF cards through Jade software, the XRD analysis of 5 vol.%, 10 vol.%, and 15 vol.% AlFeNiCrCoTi0.5p/6061Al composites was carried out to understand the phase composition of the materials. As shown in Figure 4, with the increase in HEA volume, there was no change in the phase structure of the composite material. However, the presence of the Al element promoted the formation of the BCC structure. The FCC structure was reduced and the BCC structure was increased, which improved the material strength.

The (AlFeNiCrCoTi0.5)p/6061Al matrix composites with high-entropy alloy contents of 0 vol.%, 5 vol.%, 10 vol.%, and 15 vol.% were analyzed by SEM scanning, and the EDS line scanning and surface scans were used to differentiate and study the composition and morphology of the composites. Figure 5a shows the 6061 Al matrix without HEA reinforcing particles, and the dark area was the pore defect in the material; the dark area in Figure 5b–d was the Al matrix, and the brighter area represents HEA particles. Comparing the changes in Figure 5a,b, it could be seen that the introduction of HEA particles reduced the defects in the Al matrix; the HEA particles in Figure 5b,c were evenly distributed, but the partial enlarged images showed that the HEA particles themselves had cracks caused by mechanical alloying, which would reduce the strengthening effect. This is a problem worthy of attention in future research. If the HEA content increased to 15 vol.%, the agglomeration reduced the strengthening effect. As a result, composite material with a content of 10% had better properties.

The EDS line scan with 10% HEA content is shown in Figure 6. The interface between the AlFeNiCrCoTi0.5 high-entropy alloy and 6061 aluminum alloy matrix was analyzed by energy spectrum analysis. As can be seen from

Table 4. Elemental analysis results of 10 vol.% HEA composites by EDS (at. %, atom fraction).

Point/Elements	Al/%	Fe/%	Ni/%	Cr/%	Co/%	Ti/%
1	73.07	6.12	5.97	5.59	5.51	3.74
2	20.42	17.03	17.24	15.64	19.69	9.99

, the highest volume element is Al, which accounts for 73.07%, while other elements account for about 5%. There was a transition layer between HEAs and 6061Al. As can be seen from Figure 7, HEA-reinforced particles were well combined with the aluminum matrix, and no obvious gap was generated.

The composite materials containing 10% AlFeNiCrCoTi0.5 by volume fraction were analyzed by SEM and EDS. As shown in Figure 8, the white area was the AlFeNiCrCoTi0.5 reinforcement wrapped by the dark Al matrix. The element diagram proves that there were no obvious precipitates at the interface between AlFeNiCrCoTi0.5 and the Al matrix, while the elements in HEAs were evenly distributed. Combined with the EDS analysis in Figure 6 and Table 4, the elements of Al and HEAs have diffused to a certain extent. The content of the Al element in HEAs was much smaller than that of the matrix, which caused the surface scan to fail to display. The material’s interface was well combined, and the toughness was improved.

The composite material with a content of 10 vol.% was extruded according to different passes, and the influence of the hot extrusion process on material phase transformation was understood through XRD analysis, as shown in Figure 9. As can be seen from the figure, AlFeNiCrCoTi0.5p/6061Al after hot pressing sintering only contained the enhanced phase and Al matrix, and changing the extrusion pass would not change the phase structure of the material.

The surface morphology of the composite material was further observed by SEM to understand the microstructure changes of the material after different extrusion processes, as shown in Figure 10. The increase in extrusion temperature increased the flow energy of the material, and the increase in extrusion channels caused the particles to break and be refined, so that the material was more uniform and dense. Under the shear force of extrusion for one pass (relative density of 97.63%), the oxide film on the particle surface was broken. The particles were closely bonded and the pores were reduced and refined; the surface morphology of the composite material was further observed by SEM to understand the microstructure changes of the material after different extrusion processes, as shown in Figure 10. The increase in extrusion temperature increased the flow energy of the material, and the increase in extrusion channels caused the particles to break and be refined, so that the material was more uniform and dense. Under the shear force of extrusion for one pass (relative density of 97.63%), the oxide film on the particle surface was broken. The particles were closely bonded and the pores were reduced and refined. Increasing the extrusion pass can continue to compact the material. It was worth noting that, after three passes of extrusion, some internal cracks of HEAs were fractured. HEA grains were refined by crack splitting. However, pores appeared in the separated high-entropy alloys.

Through the experimental summary, increasing the content of AlFeNiCrCoTi0.5 particles did not change the phase composition of the composites. The Al element promoted the increase in the BCC structure and improved the strength of the material. HEA particles reduced the pores and cracks inside the composite material, but agglomeration occurred with the increase in its volume fraction. HEA particles with a volume fraction of 10 vol.% had a better strengthening effect. There was a certain degree of element diffusion between the high-entropy alloy particles and the matrix interface. At the junction, there were no obvious precipitates and cracks. Increasing the extrusion pass can reduce the porosity of the material, thus improving the hardness and strength of the material. However, too many extrusion times would lead to broken HEA particles. AlFeNiCrCoTi0.5 high-entropy alloy particles with a volume fraction of 10% were more suitable as a reinforcer after extrusion for two passes and 90 h ball milling alloying.

4. Mechanical Property Analysis

The tensile properties of AlFeNiCrCoTi0.5p/6061Al with HEA volume fractions of 5 vol.%, 10 vol.%, and 15 vol.% were measured at room temperature (26 °C), as shown in Figure 11. Compared with the 6061 Al alloy, the tensile strength of the composite material was increased by 7.2% when the AlFeNiCrCoTi0.5 was 5 vol.%. If AlFeNiCrCoTi0.5 was 15 vol.%, the tensile strength increased by 38.4%. With the increase in high-entropy alloy particles, the tensile strength of the material increased significantly. If the AlFeNiCrCoTi0.5 was 10 vol.%, the elongation decreased by 7.4%. When AlFeNiCrCoTi0.5 was 15%, the material elongation rapidly decreased. With the increase in HEA particles, the elongation of the material and the plasticity decreased. HEAs could strengthen the aluminum matrix by refining grains and hindering the movement of dislocations. Therefore, when AlFeNiCrCoTi0.5 was 10 vol.%, the composite had good comprehensive mechanical properties.

After multiple extrusions, the hardness of the composite material containing a content of 10 vol.% AlFeNiCrCoTi0.5 was measured, as shown in Figure 12. After two passes of extrusion, the hardness of the material increased by 3.3%. The tensile strength of the composites increased most significantly when the composites were extruded for three passes. The hardness of composites increased slowly with the increase in the number of extrusion passes. With the increase in the number of equal diameter angular extrusion passes, grains were refined and subgrains appeared. More grain boundaries hindered the movement of dislocations [21]. The strengthening phase was closely combined with the matrix, while the strength of the material was improved. A large number of grain boundaries overlapped and dislocations became entangled with each other, which led to the hardening of the material. The composite material reduced the plasticity [22].

(AlFeNiCrCoTi0.5)p/6061Al with a volume fraction of 10% was observed by transmission electron microscopy to further analyze the microstructure of the material, as shown in Figure 13. As can be seen from Figure 13a, elongated grains appeared in selected regions of the material. It was found that the grains with similar grain widths showed good plasticity FCC structure. During the material was heated and extruded, the grains flowed axially under the influence of the mold, and the plastic deformation caused the grains to be elongated. Considering the difference in the strength and toughness of the Al matrix and the HEAs reinforced particles, this deformation led to an increase in dislocations. In Figure 13b,c, the strength and toughness of HEAs and the Al matrix were different. As the material moved within the material, the dislocations increased and crossed, causing them to intertwine and overlap. At the same time, the hard strengthening phases were separated and the grains were refined by the transfixion mechanism of dislocation movement. Subgrains appeared in the Al matrix as a result of the dislocation motion in Figure 13d. In Figure 13c–f, subgrains and a large number of dispersed particles appeared in the Al matrix, which effectively hindered the boundary movement. At the boundary of the two phases, the stepped slip band and a large number of internal linear dislocations could share the load, which also improved the strength and toughness of the material, as shown in Figure 13f. During hot extrusion, refractory hard particles formed heterogeneous nuclei, which promoted recrystallization under the stimulated nucleation (PSN) effect. The second-phase particles (>1 μm) were driven by dislocation and accelerated the recrystallization of surrounding grains by means of dislocation energy and thermal energy [23,24,25]. The particle size of the high-entropy alloy AlFeNiCrCoTi0.5 reinforced particles was greater than 1 μm. Through the PSN effect, AlFeNiCrCoTi0.5 particles could promote the recrystallization of surrounding grains under the action of dislocation drive and deformation energy. The subgrain (boundary < 10°) produced by recrystallization produced a pin effect and short grain boundary, which caused crack dissociation and hindered crack diffusion.

Hot extrusion produced work hardening, which enhanced the deformation resistance and increased the hardness. After a certain number of extrusions, the interior of the composite material was compact and full of stress, which made it difficult for the hardness to increase again. As shown in Figure 12, the hardness of the material increased slowly after four extrusions.

Combined with Figure 14 and Figure 15, the tensile properties of 10 vol.% (AlFeNiCrCoTi0.5)p/6061Al material at room temperature (26 °C) after multiple equal angular extrusions were analyzed. It can be seen from Figure 14 that the tensile strength of the material increased obviously when the material was extruded for three passes, which was consistent with Jiang’s result of improving material strength through the extrusion method [21]. Figure 15 shows the stress–strain curve of the material after increasing the number of extrusions. After the first and second extrusion, the slope of the curve was larger after the yield stage, and the material had higher plasticity. After the material was stressed, the internal grain was broken and refined, while internal cracks decreased and crossed directions. The bonding strength of the interface was improved. After three and four extrusions, the slope of the material curve was small. At this point, the internal stress of the material was concentrated, while a large number of dislocations and slip bands occurred in the grain or at the grain boundary, which caused the material to easily split under stress and the plasticity to decrease significantly.

The tensile fracture morphology analysis of 10 vol.% (AlFeNiCrCoTi0.5)p/6061Al material after multiple equal-diameter angular extrusions is shown in Figure 16. There were many dimples in the material section, which were ductile fractures. After increasing the number of extrusion passes, the material’s cracks were passivated and the size of the dimples was reduced. Figure 16a shows that the original cracks in the material became smaller during the first extrusion. Figure 16b–c shows that, by increasing the extrusion pass, the HEA particles were broken and refined, while the cracks were compressed. Figure 16d indicates that the fracture dimple size of the material was greatly reduced after four passes of extrusion. At this time, the interior of the material was compact, which reduced the plasticity. In addition, with the increase in extrusion passes, the increase in the deformation degree also improved the work-hardening effect. The excessively intersected grain boundaries hindered the movement of dislocations. The plasticity of the material was further reduced by these phenomena. As a result, the material had a good unity of strength and plasticity after two extrusion passes.

The increase in HEAs enhanced the tensile strength of the material, but too many HEAs reduced the plasticity. If the volume ratio of AlFeNiCrCoTi0.5 was 10 vol.%, the strength of the composite increased and the plasticity was guaranteed. After increasing the extrusion pass, the hardness of the material increased. At this time, not only a large number of sub-grain and dispersed particles, but also many superimposed slip bands and dislocations, appeared in the material. The enhancement effect of HEAs was significant. After extrusion treatment, the strength of the material continued to improve. Moreover, the plasticity of the composites was firstly improved with the refinement of particles and the increase in grain boundaries produced by extrusion, and then decreased with the effect of work hardening. In the fracture morphology of the material, the cracks were weakened as a result of the increase in the number of extrusions, while the size of the dimples continued to decrease. Therefore, the two-pass extrusion treatment was beneficial to ensure the comprehensive mechanical properties of the material.

5. Conclusions

The structure of 6061 Al reinforced with AlFeNiCrCoTi0.5 high-entropy alloy particles prepared by mechanical alloying is changed, while its mechanical properties are improved after cold isostatic pressing and hot extrusion:

(1)

AlFeNiCrCoTi0.5 high-entropy alloy particles can be prepared by mechanical alloying, with Al being alloyed first. A dual-phase structure appeares when the alloying time is 70 h. After the processing time reaches 90 h, the lattice distortion and dislocation increase, while the solid solution structure of FCC + BCC is formed. The reinforcing particles that are uniformly distributed have a good strengthening effect.

(2)

After the equal-diameter angular extrusion, the elements diffuse, and the interface of (AlFeNiCrCoTi0.5)p/6061Al composite is tightly combined without cracks. High-entropy alloy reinforcement with a volume of 10% has the best strengthening effect on 6061 Al. At this time, the composite material has good comprehensive properties, with hardness of 70.3 HV, tensile strength of 188.1 MPa, and elongation of 14.1%.

(3)

The increase in the number of extrusion passes refines the internal structure of the material and reduces the number of pores in the Al matrix and between the HEAs–Al interface. The strength and hardness of the composite increase, while the plasticity decreases; if the number of extrusion passes is two, the material properties reach a balance, not only improving the strength, but also ensuring plasticity.