Heat-treatment Process of a New High Zinc Al-Zn-Mg-Cu Alloy

Abstract

A kind of Al-Zn-Mg-Cu alloy containing 9.6%(mass fraction) Zn element was produced by the Hot-top semi-continuous DC casting technology. The microstructure of the alloy and the temperature of phases transformation were investigated by optical microscopy(OM),transmission electron microscopy(TEM) and differential scanning calorimetry(DSC) respectively.The hardness and tensile properties of the alloy were tested,and the fracture was studied by scanning electron microscopy(SEM).Results show that the as-cast microstructure of this alloy is fine and has less intergranular eutectic phases, with the melting temperature of 473.4℃. Therefore, the homogenization heat-treatment is 465℃/24h. After the homogenization heat-treatment, the grain boundary of the ingot has turned to be intermittent and the phases have dissolved significantly. Besides, the systematic experiments were conducted on the T6 and RRA of this alloy after extrusion. The results show that on the condition of 135℃/12h treatment, the highest hardness is 197.7HBS, and the tensile strength, yield strength, elongation are 727.5, 718.0MPa and 9.3% respectively. On the condition of 120℃/24h+190℃/5min+135℃/3h treatment, the highest hardness is 204.7HBS, and the tensile strength, yield strength, elongation can reach 764.0, 749.0MPa and 7.2% respectively.

Keywords

• Al-Zn-Mg-Cu alloy
• heat-treatment
• aging
• mechanical property