Aging behavior of Al-4.5%Mg, Al-4.5%Mg-0.35%Mn and Al-1.3%Mg-1.1%Mn alloys containing 0.2%Cu

Abstract

Aging behavior of solution-treated and cold-rolled Al-4.5%Mg, Al-4.5%Mg-0.35%Mn and Al-1.3%Mg-1.1%Mn alloy sheets containing 0.2%Cu was investigated by tensile test and electron microscopy. The alloy samples were isochronally aged at temperatures between room temperature and 300°C for 20s or isothermally aged at 220°C for 5 to 18000s. The decrease in the mechanical strength at higher temperatures than 260°C or at prolonged aging time longer than 1200s is suppressed by reducing the amount of Mn addition and increasing homogenization temperature as well as solidification rate during casting. The increased volume fraction of fine Mn-baded dispersoids is found to have the effect to decrease the mechanical strength during aging. The heterogeneous precipitation of the S phase (Al₂CuMg) on the fine Mn-based dispersoide is found to occur in the solution-treated and then cold-rolled Al-1.3%Mg-1.1%Mn-0.45%Cu alloy sheet aged at 240°C for 2h.