Interaction of steel with pure Al, Al-7Si and A356 alloys

Carbon steel bars were dipped in aluminum alloy melts for different periods of time. A reactive iron-aluminum intermetallic layer grew at the interface between the melt and the steel substrate. This reactive layer was mainly composed of intermetallic Fe-Al (Fe₂Al₅) and its thickness was influenced by dipping time (3-60 min), surface roughness (0.74 μm versus 0.07 μm) and carbon content (0.2-0.4 wt%) of the steel bars and the elements (mainly Si and Mg) added in the aluminum alloys. An oxide film, which existed at the interface between steel bar and melt, hampered the Al-Fe reaction. In comparison with a pure Al melt, the thickness of the reactive layer of the Al-7Si alloy melt decreased after a very short dipping time (3 min), increased following an increase in the dipping time (10 min) then decreased after a long dipping time (>20 min). The thickness of the reactive layer of a 1040 steel bar dipped in an A356 alloy (Al-7Si-0.4Mg) melt for a given dipping time at 973 K, was the narrowest among all melts studied; including pure Al, Al-7Si, Al-1Mg and Al-7Si-0.4Mg alloys.