**Experimental and Numerical Study on Microstructure and Mechanical Properties of Ti-6Al-4V**/**Al-1060 Explosive Welding**

#### **Yasir Mahmood, Kaida Dai \*, Pengwan Chen \*, Qiang Zhou, Ashfaq Ahmad Bhatti and Ali Arab**

State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing 100081, China; 3820160003@bit.edu.cn (Y.M.); zqpcgm@gmail.com (Q.Z.); ashfaqb@live.com (A.A.B.); arabali83@yahoo.com (A.A.)

**\*** Correspondence: daikaida@bit.edu.cn (K.D.); pwchen@bit.edu.cn (P.C.); Tel.: +86-010-6891-8740 (K.D. & P.C.)

Received: 15 October 2019; Accepted: 2 November 2019; Published: 5 November 2019

**Abstract:** The aim of this paper is to study the microstructure and mechanical properties of the Ti6Al4V/Al-1060 plate by explosive welding before and after heat treatment. The welded interface is smooth and straight without any jet trapping. The disturbances near the interface, circular and random pores of Al-1060, and beta phase grains of Ti6Al4V have been observed by Scanning electron microscopy (SEM). Heat treatment reduces pores significantly and generates a titanium-island-like morphology. Energy dispersive spectroscopy (EDS) analysis results show that the maximum portion of the interfacial zone existed in the aluminium side, which is composed of three intermetallic phases: TiAl, TiAl2 and TiAl3. Heat treatment resulted in the enlargement of the interfacial zone and conversion of intermentallic phases. Tensile test, shear test, bending test and hardness test were performed to examine the mechanical properties including welding joint qualities. The results of mechanical tests show that the tensile strength and welding joint strength of the interfacial region are larger than one of its constituent material (Al-1060), the microhardness near the interface is maximum. Besides, tensile strength, shear strength and microhardness of heat treated samples are smaller than unheat treated. Smooth particle hydrodynamic (SPH) method is used to simulate the transient behaviour of both materials at the interface. Transient pressure, plastic deformation and temperature on the flyer and base side during the welding process were obtained and analyzed. Furthermore, the numerical simulation identified that almost straight bonding structure is formed on the interface, which is in agreemen<sup>t</sup> with experimental observation.

**Keywords:** explosive welding; Ti6Al4V/Al-1060; microstructure; mechanical properties; smooth particle hydrodynamic (SPH)
