Influence of Cu and Mn content on the properties of Al-Mg4.5-(Mn,Cu) type alloy sheets

Abstract

Influence of Cu and Mn content on the grain structure, precipitation effects and mechanical properties of two Al-Mg4.5-(Mn,Cu) type sheets was considered. It was found that a variety of grain size can be obtained in alloy with no Mn after different annealing conditions. In Mn-containing alloy the grain growth was suppressed by Mnbearing particles and the grain size was not affected by the annealing temperature. The presence of 0.52 % Mn brought an appropriate strength increase (ΔYS ≤ 30%, ΔUTS ≤ 10%), but the ductility was not influenced by Mn content. The electrical resistivity used to follow precipitation/dissolution processes was mostly affected by precipitation or dissolution of Cu-bearing precipitates, which were found dominantly formed during the interstage recrystallization annealing. During final annealing sizeable change of the electrical resistivity was noticed only after high temperature annealing (as 470°C) when intensive dissolution occurs. The ageing response of the tested alloys was effective after ageing treatment at 140°C and 160°C. The high ageing potential of alloy I, with Mn and higher Cu content, was assumed to be due to higher content of Cu/Mg clusters and S' (Al2MgCu) phase particles. Since the age hardening effect was effective even at 140°C, this type of alloys becomes suitable for paint baking procedure at lower temperatures than the currently used of 160°-180°C.