Novel approach in manufacturing aluminum-based alternate layered composite material via friction stir additive manufacturing route

The majority of today's metal additive manufacturing techniques involve the transition of phases from liquid to solid, affecting their performance due to the microstructures formed during solidification. Employing novel solidstate additive manufacturing techniques like friction stir additive manufacturing (FSAM) helps to overcome these constraints. This study employed alternative layers of AA 6061-T6 and AA 7075-T6 aluminum alloys to construct defect-free alternate layered composite material (ALCM) via FSAM route using a single-pass (SP) weld strategy and double-pass (DP) weld strategy. The experiments were conducted by selecting the tool traverse speed, tool rotation speed and tool tilt angle as 40 mm/min, 1200 rpm and 2 degrees when AA 6061-T6 was set over AA 7075-T6 and 50 mm/min, 1100 rpm and 2 degrees when AA 7075-T6 was set over AA 6061-T6. A comprehensive investigation of the mixing of these dissimilar materials, changes in microstructure and microhardness, and variations in strength along the longitudinal direction in the stir zone (SZ) are evaluated in this study. Microstructures that evolved during both strategies were observed to be non-uniform, and equiaxed refined grains were identified in the SZ, which was recognized as the build's most functional part. Repetitive stirring by the rotating tool decreased the average grain size and low-angle grain boundaries (LAGBs) along the SZ. The hardness and strength in the final build increased from lower layers to upper layers primarily due to the variation in grains and precipitate size. The highest value of hardness of 215.7 HV was identified in the topmost layer of DP technique, which was 15% higher when compared with the SP technique. Similarly, a 15% increase in strength was also observed in the topmost slice in the DP technique, whose value corresponds to 364 MPa. This study presents a summary of the results indicating that the use of a composite material consisting of alternating layers of AA 6061-T6 and AA 7075-T6 materials, which possess enhanced hardness and tensile strength, may serve as a viable replacement for the typical AA 6061 material often employed in automotive components. This substitution offers the potential for improved performance and increased lifespan.