Effects of processing variables and heat treatments on Al/Ti-6Al-4V interface microstructure of bimetal clad-plate fabricated via a novel route employing friction stir lap welding

摘要

Al/Ti-6Al-4V bimetal clad-plates were fabricated via a novel process route employing multi-pass friction stir lap welding (FSLW) method. The process feasibility, effects of processing parameters and post heat anneal treatments on macro formability, Ti/Al interface layer microstructures and bonding strengths of the produced clad-plates were investigated. A Ti/Al metallurgical bonding interlayer at the clad-plate interface location, with good densification and considerable thickness, was obtained under the optimized FSLW process condition. Following the research on the influences of FSLW processing variables on the produced Ti/Al interlayer structure, the thermal-mechanical effect, as the main formation mechanism, was further discussed. It was revealed that the post anneal at 400 degrees C-600 degrees C for 1 h duration generated a diffusion-dissolution layer of multi-island-shaped Al-Al3Ti dual phase structure at the Al/Ti-6Al-4V interface. A well composition-homogenized diffusion-dissolution interlayer with good interfaces between multi-island-like Al and its adjacent Al3Ti phase regions improved the Al/Ti-6Al-4V clad-plate bonding strength. The laminated microstructure of Ti/Al interlayer produced by FSLW exerted a prehomogenization effect on shortening Ti/Al diffusion distance during the post anneal. (C) 2015 Elsevier B.V. All rights reserved.