Achieving superior dispersion-strengthening effect in an AA5xxx Al-Mg-Mn alloy by mico-alloying

Abstract

5xxx Al-Mg based alloys are widely applied as non-heat-treatable alloys. In this work, we designed a dispersion-strengthening Al-4Mg-1Mn-0.3Fe-0.2Si-0.2Zr-0.2Cr (wt.%) alloy. By applying ramp heating and 400 °C isothermal aging, a significant dispersion-strengthening effect through the formation of various types of dispersoids was achieved. Detailed scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis revealed the precipitation behaviors of nanoscale Mn-rich dispersoids and Al3Zr nanoparticles during heat treatments. As a result, an increment of 48 MPa in yield strength was obtained compared with the reference 5182 alloy. Meanwhile, the modified alloy shows a good heat resistance at 400 °C with little loss of yield strength until 200 h of heating. This has been attributed to the further precipitation of Al3Zr particles which counteracts the coarsening of Mn-rich dispersoids. Moreover, the addition of peritectic element Cr was found to significantly promote the precipitation of Al6(Mn,Fe,Cr) in dendritic center regions, thus improving their global distribution across dendrite arms. The presence of dense dispersoids can also improve the recrystallization resistance of the deformed alloy during annealing, thus retaining the deformation fiber structure and significantly retarding the recrystallization behavior. This research demonstrates an effective strategy to develop high-performance 5xxx series alloys strengthened via dispersoids.