In situ formation of various intermetallic particles in Al–Ti–X(Cu, Mg) systems during friction stir processing

In situ Al composites reinforced by various intermetallic particles were fabricated from Al–Ti–X(Cu, Mg) systems by hot pressing, forging and subsequent 4-pass friction stir processing (FSP). The formation of various intermetallic particles during FSP and the tensile properties of in situ composites were investigated. For Al–Ti–Cu system, Cu enhanced the Al–Ti reaction and resulted in the formation of more Al3Ti particles due to the presence of a small amount of liquid phase during FSP. After FSP, part of Cu was kept in the Al matrix as solute, whereas the other formed Al2Cu particles. For Al–Ti–Mg system, except for Al3Ti, some Ti2Mg3Al18 particles with fine twin lamellas were formed during FSP, resulting in an increase in the total volume fraction of reinforcing particles. Cu and Mg addition increased the strength of the in situ composites substantially due to introduction of more strengthening modes and more reinforcing particles, however the elongation decreased dramatically.