Interface chemistry in aluminium alloy castings reinforced with iron base inserts

Bimetallic automotive components consisting of an Al–Si light alloy reinforced with a cast iron insert have been manufactured by gravity die moulding. Special precautions have been taken to ensure a uniform wetting of the insert by the liquid light alloy. Under these conditions, three intermetallic compounds are formed at the insert/alloy interface: η (Al 5Fe 2), τ5 (Al 7.4Fe 2Si) and τ6 (Al 4.5FeSi). Upon subsequent heat-treatment, τ2 (Al 5Fe 2Si 2) and τ10 (Al 12Fe 5Si 3) also appear. Growth of these compounds is discussed in terms of thermodynamics, kinetics and reaction mechanism in the Al–Fe and Al–Fe–Si systems. The effect of these chemical changes on the mechanical properties of the insert/alloy joint will be examined.