Mechanical properties of self-hardening Al-Zn-Si cast alloy with higher content of Fe

Abstract

Recycled (scrap-based) aluminium alloys are commonly referred to as secondary. In cast aluminium components, brittle and needle/plate-like Fe-rich particles are common constituents that normally degrade the mechanical properties. Secondary Al-alloys contain higher background Fe levels than the primary metal and is currently no economical way of removing Fe. Therefore, it is important to gain knowledge on the effect of Fe-rich particles on mechanical properties in order to expand the use of more environmental friendly secondary alloys. Present study examines the effect of iron phases Al5FeSi in secondary self-hardening AlZn10Si8Mg cast alloys A (0.15 wt% Fe) and B (0.56 wt% Fe) on microstructure, mechanical properties (UTS, YTS, ductility and Brinell hardness) and fracture surfaces. For observation and identification of microstructural components as Si and Fe-phases standard (0.5% HF) and deep etching (HCl) were utilized. The results showed that the eutectic silicon in alloy B has a slightly finer structure (probably due to slightly higher cooling rate used); with increasing of the Fe content, the length and number of Al5FeSi phases increased too; mechanical properties slightly decreased (YTS from 175 MPa to 166 MPa and UTS from 187 MPa to 178 MPa). The fracture surface of experimental samples mainly consists of transcrystalline ductile fracture (the transcrystalline cleavage fracture was not detected as much). In alloy A dominant is the transcrystalline ductile fracture in the eutectic and on the α-matrix and in alloy B is dominant the transcrystalline cleavage fracture.