Fatigue strength of friction stir lap welded AA2024 to Ti6Al4V dissimilar joints

Abstract

Fatigue testing has been conducted on welds of AA2024 (Al4.5Cu1.4 Mg0.5Mn) alloy to Ti6Al4V alloy made using friction stir lap welding (FSLW). During FSLW, pin bottom aimed for touching the Ti6Al4V plate (dPin≈0), although it could readily penetrate (dPin > 0). It has been found that fatigue limit of the AA2024/Ti6Al4V welds was slightly higher than the fatigue limits of the FSL Al-to-Al alloy welds reported in literature. Examination has demonstrated that forming a very thin interface layer during FSLW was the major mechanism responsible for the good fatigue strength. The diffusion weld distance outside the pin width in dPin > 0 welds was significantly larger than that in dPin≈0 welds. Thus, the fatigue limit of dPin > 0 welds was comparable to the fatigue limit of dPin≈0 welds despite of the mix stir zone (MSZ) in dPin > 0 welds being a brittle one. The different thermomechanical conditions for the different diffusion-weld widths will be illustrated.