**2. Materials and Methods**

The composition of the alloy prepared in this experiment is 20.0 wt.% Sn, 2.0 wt.% Cu, with the remainder of the material comprising Al. The purity of all raw materials is above 99.9%. The software PANDAT (CompuTherm LLC, Middleton, WI, USA) was used to calculate the equilibrium phase diagram of the AlSn20Cu alloy and the results are shown in Figure 1. Figure 1a shows the phase transition with increasing Sn content in Al–2Cu matrix, and Figure 1b shows the phase transition with increasing Cu content in Al–20Sn matrix. Tin and aluminum cannot dissolve each other in the solid state, they both maintain the original phase structure. Copper is present in the aluminum matrix (FCC\_Al) in the form of Al2Cu (AlCu\_Theta).

Spray forming is conducted using SF-500 equipment (GRIMAT Ltd., Beijing, China), which is a self-made machine. The schematic diagram of SF-500 equipment for spray forming is shown in Figure 2. Semi-continuous casting and semi-solid die casting was conducted using universal equipment. A metallographic microscope and scanning electron microscope (SEM) are used to observe the microstructures of the alloys. Image processing software (ImageJ software, National Institutes of Health & Laboratory for Optical and

Computational Instrumentation, Madison, WI, USA) is used to analyze the morphology of the Sn phase.

**Figure 1.** The equilibrium phase diagram of the AlSn20Cu alloy calculated by PANDAT: (**a**) the phase transition with increasing Sn content in Al–2Cu matrix, (**b**) the phase transition with increasing Cu content in Al–20Sn matrix.

**Figure 2.** Schematic diagram of the spray-forming process.

The AlSnCu alloy ingot prepared by semi-continuous casting is cylindrical, which needs to be rolled and heat treated to form the plate for making the bearing bush. Gleeble compression experiments were used to study the process parameters of rolling deformation. The compression experiment temperature is 20, 100, 150, 202, 222, and 242 ◦C; the strain rate is 0.01, 0.1, and 1 s−1; the deformation is 60%; and the quenching and cooling are realized within 3 s after deformation. The AlSnCu alloy ingot prepared by semi-solid die casting is flat, which reduces the production process of the bearing bush. The AlSnCu alloy

ingots prepared by spray forming are also cylindrical. Because there are many defects in it, it needs to be reduced by densification process, and finally the ingot is sliced into plates.
