Research on the microstructure, fatigue and corrosion behavior of permanent mold and die cast aluminum alloy

• Corrosion resistance of die cast AlMg5Si2Mn is superior to that of permanent mold sample.
• Corrosion and pitting potential of AlMg5Si2Mn is around −1220 mV and −690 mV.
• The application potential of die cast AlMg5Si2Mn in marine industry is confirmed.
• Fine size microstructure and defects are responsible for the different mechanical properties.
• Fe-rich particles deteriorate the tensile and fatigue strengths of permanent mold specimens.

Permanent mold (PM) and high pressure die cast (HPDC) AlMg5Si2Mn are employed to investigate the microstructure, fatigue strength and corrosion resistance. Results indicated that the mechanical properties (Rm, R0.2 and δ) of HPDC specimens (314 MPa, 189 MPa and 7.3%) are significantly better than those of PM specimens (160 MPa, 111 MPa and 2.5%) due to the finer grain size and less cast defects. Fatigue cracks of PM samples dominantly initiated from shrinkage pores and obscure fatigue striations are observed in crack growth region. Corrosion and pitting potentials of PM and HPDC AlMg5Si2Mn alloy are around −1250 mV, −760 mV and −1220 mV, −690 mV respectively. Numerous pits are observed around the grain boundaries because the corrosion potential of Mg2Si is more anodic than that of α-Al matrix. In addition, the superior corrosion resistance of HPDC samples can be attributed to the fine grain size and the high boundary density which improved the formation of oxide layer on the surface and prevented further corrosion.