Effect of overlapping region on double-sided friction stir welded joint of 120 mm ultra-thick SiCp/Al composite plates

Abstract

Effective joining techniques are urgent and necessary for the rapid developments and widespread applications of aluminum matrix composite (AMC) components. Friction stir welding (FSW) is a very promising method for joining AMCs without clear defects, while double-sided FSW is especially preferred in joining thick or ultra-thick AMC plates. The overlapping region stirred twice by the two welding passes is formed during the double-sided FSW, which has an important effect on the microstructures and mechanical properties of the composite joint. In this work, 120 mm ultra-thick plates of 16 vol % SiCp/2014Al composites were successfully joined by the double-sided FSW, and an overlapping region appearing at the middle thickness of the composite joint is mainly concerned and studied. Compared with the base material and the region stirred once in the SiCp/Al composite joint, the decrease of SiC particle size, improved uniformity of particle distribution and refinement of aluminum grains and precipitates are observed in the overlapping region as a result of repetitive mechanical stirring during the double-sided FSW. The overlapping region exhibits the largest Vickers hardness and overall tensile properties: yield strength of 224 MPa, ultimate tensile strength of 369 MPa and failure elongation of 6.6%. The simultaneous enhancement in tensile strength and ductility in the overlapping region is attributed to the more effective load-transfer of reinforced particles with decreasing particle size, and the increased grain boundary strengthening due to matrix grain refinement. A comprehensive understanding the effect of overlapping region on the microstructural characterization and mechanical properties of the composite joint is positive and important to promote and accelerate the industrial applications of double-sided FSW technology in joining thick or ultra-thick metal matrix composite plates.