Al-Si-Cu alloys for high pressure die casting: influence of Fe, Mn and Cr on room temperature tensile and fatigue properties

Al-Si-Cu alloys with high Fe content are widely employed in high pressure die casting (HPDC). Even if Fe is usually considered an impurity in secondary aluminum alloys, leading to the formation of harmful intermetallic compounds, it helps in mitigating or eliminating the problem of die soldering. As a result, secondary Al alloys with Fe content of about 1 wt% are commonly employed for the production of HPDC castings. Aiming to change the morphology of harmful Fe-bearing phases towards less detrimental morphologies, proper alloying elements may be added to the alloys. Mn and Cr (both present in the aluminum scrap), as instance, are reported to prevent from the formation of the acicular β-Al5FeSi phase, leading to the formation of more compact and polygonal intermetallics. Such phases are usually referred to as “sludge” particles. The influence of sludge particles on mechanical properties of Al-Si-Cu castings is still under investigation. The present work aims at evaluating the effect of impurities (Fe, Mn and Cr) typically present in secondary Al alloys on the microstructure and mechanical properties of the A380 (Al-Si-Cu) alloy. Samples with different Fe, Mn and Cr content were produced and processed through a directional solidification equipment to obtain specimens with controlled SDAS (~10 μm). Hardness and rotating bending fatigue tests were carried out at room temperature. Mechanical properties of the alloys were then related to the microstructure, analyzed by optical and scanning electron microscopy