Influence of interface reactions on fracture mechanisms in TIG arc-welded aluminium matrix composites

This paper describes the influence that the interfacial reaction between the matrix and reinforcement has on the fracture behaviour of an aluminium alloy (2014) reinforced with SiC particles when it is arc welded. TIG arc-welding tests were carried out on 4-mm thick sheets of AA2014/SiC/Xp (where X is 6, 13 and 20 vol%, respectively), which were machined with the welding pool in the transverse position and tensile tested. In all specimens tested, the failure was located in the weld metal with a tensile strength lower than 50% of the parent material properties. Fractures of the tested welds were studied and compared with those of the parent composites. Both surface studies of the fracture (SEM) and transverse preparations of these (LM and SEM) were observed. From these studies, it was deduced that the proportion of interfacial failure increases in the weld material because of the formation of Al4C3, which reduces the strength of the matrix/reinforcement interface, limiting the number of cracked particles. Also, embrittlement of the matrix alloy was observed, caused by the increment of Si-rich phases and intermetallic compounds in it (Si and Al–Fe–Si).