SQUEEZE CAST-ALUMINUM REINFORCED WITH MILD-STEEL INSERTS

The bonding of a mild steel insert to an AI-7Si alloy during squeeze c asting has been studied for a range of processing conditions. Assessme nt of the mild steel/Al-7Si alloy interface shear strength has been ma de with a push-out test, and the results have been correlated with mic rostructural observations and residual stress calculations. Uncoated i nserts do not exhibit any significant reaction with Al-7Si because of rapid cooling of the melt during squeeze casting, giving a low interfa ce shear strength of similar to 30 MPa. Preheating the inserts to 900 degrees C slightly improves the interface shear strength to similar to 45 MPa, but reaction between the steel and Al-7Si is prevented by the formation of an Fe3O4 magnetite layer on the steel surface. Inserts h ot-dipped in molten Al-10Fe before squeeze casting have a much greater interface shear strength of similar to 110 MPa, with failure in the A l-7Si matrix rather than at the steel/Al-7Si interface. Inserts vacuum plasma spray coated with titanium have the greatest interface shear s trength of similar to 130 MPa, without any interface reaction, because of mechanical keying of the rough splat-quenched titanium surface com bined with high residual stresses in the AI-7Si matrix.