Heat treatment of the new high-strength high-ductility Al–Mg–Si–Mn alloys with Sc, Zr and Cr additions

Abstract

Heat treatment of alloys of the Al–Mg–Si system essentially affects the age-hardening response and, accordingly, their final mechanical properties. However, the specific Mg/Si ratio in casting alloys makes age-hardening by heat treatment negligible. To improve the age-hardening response, the alloys were alloyed with Sc, Cr, Zr, and two types of heat treatment were applied: full T6 (solution treatment (ST), quenching, and artificial aging (AA)); and T5 with AA from the as-cast state. The microstructure after different heat treatment modes was observed by means of SEM and TEM. It was established that the main structural components that affect the mechanical properties of alloys after heat treatment are nanoscale precipitates and a coarse Al7Cr and Al3Zr intermetallic phases in the Cr- and Zr-containing alloys. The highest impact in terms of tensile properties was achieved in the Sc-containing alloys after T5 at 325 °C. Alloys with 0.2 wt% Sc exhibit the highest strength after T5 from as-cast state at 325 °C (up to 380 MPa) and highest elongation (up to 20%) after full T6 (ST 520 °C and AA 325 °C).