Investigation of mechanical properties of AA6082-T6/AA6063-T6 friction stir lap welds

A study is conducted to investigate the microstructure and mechanical properties of lap joints produced by friction stir welding (FSW) between 3.5 mm thick sheets of automotive aluminum alloys AA6082-T6 with AA6063-T6. The FSW tool used in this study includes a set of Wiper (TM) scrolls on the shoulder face and a probe having right hand threads, a set of tapered flats, and a set left hand CounterFlow (R) grooves. The FSW process parameters are first optimized through the use of Design of Experiments (DOE) methodology. Static lap-shear tests are performed on the DOE coupons to identify the optimized parameters and once an optimized set of process parameters is identified, lap joint coupons are fabricated from sheets of each alloy for further mechanical and metallurgical investigation. The study implemented post-weld material characterization tests alongside a novel real-time feedback signal monitoring method for assessing the properties of friction stir lap welds. The analysis included microstructural examination, microhardness testing, lap shear testing, and an advanced electronic non-destructive evaluation (e-NDE) technique that uses the process feedback forces to detect weld anomalies primarily in the form of voids in real time. The analysis includes microstructural examination, microhardness testing, lap shear testing, and an advanced electronic (signal/frequency analysis) non-destructive evaluation (e-NDE) technique in order to detect weld anomalies primarily in the form of voids. For comparison purposes, the specimens are tested under two different loading scenarios; loading of the advancing side, and loading of the retreating side. During FSW, the plasticized material is dragged by the tool from the retreating side of the weld to the advancing side around the rear of the tool. Each loading scenario is tested for three conditions; as-welded, naturally-aged, and post-weld heat treated. The weld produced by the optimized parameters was fully consolidated and had no volumetric defects; absence of hooking is clearly identified in the microstructural analysis of the dissimilar lap joint along with good material flow and mixing of the alloys. The 'advancing-side-loading' is found to perform with higher strength than the 'retreating-side-loading,' which is evidence that 'retreating-side-loading' is less favorable in the FSW lap joints produced in this study because of weaker weld strength in the retreating side. A finite element modeling procedure is utilized to examine the distribution of stresses and displacements in a shear test of a lap weld sample. This study identifies improved process parameters for friction stir welding of dissimilar aluminum alloys for enhanced performance.