The development of low-temperature heat-treatable high-pressure die-cast Al-Mg-Fe-Mn alloys with Zn

摘要

In the present work, a novel low-temperature heat-treatable recycled die-cast Al-Mg alloy was developed by adding Zn into non-heat-treatable Al-5Mg-1.5Fe-0.5Mn alloy. The results showed that Zn additions resulted in the formation of equilibrium phase T-Mg-32(Al, Zn)(49) under as-cast condition, which can be dissolved into the alpha-Al matrix at a relatively low solution temperature (430 degrees C) and thus set the base for the low-temperature heat treatment. The mechanical test results indicated that Zn additions had a smooth liner improvement in the strength of all as-cast alloys and T6-state alloys with 1% and 2% Zn as its concentration increased but resulted in a sharp improvement on the strength of T6-state alloy when Zn concentration increased from 2 to 3%. TEM analysis revealed that the precipitate in T6-state Al-5Mg-1.5Fe-0.5Mn-3Zn alloy is eta ' phase, rather than the widely reported T '' or T ' phase in other Al-Mg-Zn alloys with approximately same Mg and Zn concentrations. After the optimized low-temperature T6 heat treatment (solution at 430 degrees C for 60 min and ageing at 120 degrees C for 16 h), the Al-5Mg-1.5Fe-0.5Mn-3Zn alloy exhibits the yield strength of 321 MPa, ultimate tensile strength of 445 MPa and elongation of 6.2%.