The influence of Cu rich intermetallic phases on the microstructure, hardness and tensile properties of Al–15% Mg2Si composite

This study was undertaken to investigate the effect of different concentrations of copper (0.1, 0.3, 0.5, 1.0, 3.0, and 5.0 wt.%) on the microstructure, hardness and tensile properties of an in situ cast composite (Al–15% Mg2Si). The microstructural study of the composite showed both primary and secondary Mg2Si phases in all specimens and intermetallics containing Cu (Q and θ phases) were visible at high Cu contents. Hardness and tensile tests demonstrate that the addition of Cu increases both hardness and ultimate tensile strength (UTS) values. But that a reduction in elongation occurs with the addition of Cu (≥1% Cu). A study of the specimen's fracture surfaces via scanning electron microscope (SEM) revealed that all specimens with large facets of primary Mg2Si particles succumb to brittle fracture. These brittle phases can initiate cracks, but Cu rich intermetallics phases, produced from the segregation of Cu on eutectic cell boundaries, appear to be the favored path for crack propagation.