A STUDY OF THE MICROSTRUCTURES AND PROPERTIES OF AN A390.0 ALUMINUM-ALLOY PRODUCED BY THE LAYER DEPOSITION PROCESS

An A390.0 aluminium alloy produced by a newly developed layer depositi on process was studied regarding the refinement of microstructures and the improvement of mechanical properties. The counterpart for compari son was the same alloy but cast in an iron ingot mould. The results sh ow that silicon particles of the layer-deposited alloy are fine and un iformly distributed in the matrix. Moreover, the segregation is signif icantly inhibited. The silicon particles and segregation of the cast a lloy are very coarse. The mechanical properties of the former also exh ibit a better combination of strength and ductility. The excess disper sion strength from fine silicon particles is about 40 MPa which does n ot change with aging time to the first order. The ductility improvemen t is attributable to the fine silicon particles since they require hig her strain for void nucleation. The coarsening rate of silicon particl es is high for the layer-deposited alloy when homogenized at 495-degre es-C. This is because of the high interfacial energy possessed by the fine distribution. The coarsening is an Ostwald ripening process contr olled by volume diffusion.