Microstructures and mechanical properties of Al-Cu-Mg-(Ag,La) alloys

A series of Al-5.3Cu-0.8Mg(mass fraction,%) based alloys with different Ag and La contents were investigated by optical microscope(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM) and mechanical properties testing.The results show that adding 0.1La refines the grains of as-cast Al-5.3Cu-0.8Mg-(0.6Ag) alloys,but does not improve the hardness of the extruded Al-5.3Cu-0.8Mg alloys.Adding 0.6Ag can increase the hardness and tensile strength of extruded Al-5.3Cu-0.8Mg alloys and decrease the peak-aging time at 185 ℃.The coherent plate-like Ω phase and a small amount of θ′ phase are the predominant hardening phases of the Al-5.3Cu-0.8Mg-0.6Ag alloys at peak-aged stage at 185 ℃.Moreover,adding 0.1La into Al-5.3Cu-0.8Mg-0.6Ag alloy decreases the size and improves the density and the thermal stability of Ω phase,and then improves the mechanical properties of the alloy.