Fast aging strengthening by hybrid precipitates in high pressure die-cast Al-Si-Cu-Mg-Zn alloy

Abstract

The improvement on mechanical properties in high pressure die casting (HPDC) Al Si alloys is an important issue for their application. In this present study, it is found that the artificial aging with low-temperature and short-time can remarkably improve the mechanical properties of HPDC Al-Si-Cu-Mg-Zn alloy, which can avoid heat-treatable defect formation of HPDC Al alloy and be applied in industrial production. The experimental results indicate that the as-cast microstructure of HPDC Al-Si-Cu-Mg-Mn-Zn alloy shows uniformly-distributed GB phases, fine grains and fine AlFeMnSi granular phases. Ascribed to the high cooling rate of HPDC, significant refinement of the obtained microstructure can be achieved. In addition, with the increase of aging temperature from 160 to 220 °C, the θ′ nanoscale phase can be sufficiently precipitated which results in the formation of hybrid precipitates, thus providing a better strengthening effect. The short-time artificial aging at 220 °C for 30 min remarkably improves the hardness of alloy from 115 to 145 HV with an increment of 26.1%. It is found that the hybrid precipitates including β″, Q′ and θ′ are believed to be responsible for such high strengthening contribution by superimposed strengthening in Al-matrix. The Cu-containing nano-precipitates are considered to promote the strengthening of short-time artificial aging in the HPDC Al-Si-Cu-Mg-Zn alloy. The present study provides a feasible and high-efficiency method to prepared HPDC alloy with excellent mechanical properties. • Aging-hardening behavior of HPDC Al-Si-Cu-Mg-Zn alloy was investigated. • Precipitation sequence of aging HPDC Al-Si-Cu-Mg-Zn alloy was elucidated. • Significant improvement on hardness (26.1%) was achieved due to hybrid precipitates. • Precipitation hardening effect on aging HPDC Al-Si-Cu-Mg-Zn alloy was revealed.