7075 ECO-Al Alloy with Improved Fatigue Strength of over 300MPa

One of key factors for the fatigue strength of Al alloys is to control defects in them. Among various kinds and types of defects, Mg related oxides and inclusions are most difficult-to-control defects in Al alloys. It is well known that Mg, which is one of main alloying elements in Al alloys with solid solution strengthening effect, is easily oxidized and reacted with SiC or graphite crucibles to generate oxides and inclusions, which in turn decrease abruptly ductility, fracture toughness, fatigue strength and also process-ability such as fluidity and formability.

The concept of ECO-Al alloy is to add Mg + Al₂Ca instead of Mg as an alloying element for Al alloys. Without Be addition and under ambient atmosphere through conventional processes, the addition of Mg + Al₂Ca can give us controlled oxidation during meting and holding, minimized fluidity drop during casting, and controlled oxide layer for products for Al alloys even with higher Mg content.

This paper will address the improved fatigue strength of extruded 7075 ECO-Al alloys with about 2.5wt%Mg as an alloying element and with about only 200 and 300ppm Al₂Ca. Al₂Ca can’t but be added together to Al alloys with Mg. The improved fatigue strength will be discussed in terms of improved cleanliness and refined grains due to the presence of Al₂Ca.