Effect of Mg content on mechanical properties and microstructure of Al-4.8Cu-xMg-1.0Ag alloys

The effect of Mg content on the mechanical properties and microstructure of Al-Cu-Mg-Ag alloys was characterized by means of macrohardness test,fatigue crack growth test,scanning electron microscopy(SEM) and transmission electron microscopy(TEM).The results show that: with the increase of Mg content,the aging response rate is accelerated,whereas the hardness increases at first and then decreases.And when Cu/Mg mass ratio approaches 6,the alloy has the highest hardness.TEM results reveal that the raising of Mg content promots the nucleation of the Ω phase,makes the precipitations to be smaller and finely dispersed.In addition,after aging at 165 ℃ for 30 min,the alloy with a Cu/Mg mass ratio close to 4 has the best fatigue crack growth resistance.