The AZ91/AlSi17 bimetallic samples were formed using the compound casting method. The AZ91 magnesium alloy was top-poured onto an AlSi17 aluminum alloy insert placed in a steel mould. Two types of AlSi17 inserts, differing in microstructure, were used in this study. The insert cut from an AlSi17 alloy ingot had a microstructure with irregularly shaped and unevenly distributed, large primary Si particles. The AlSi17 alloy was cast in a cold steel mould to refine the primary Si particles. In the other insert, cut from rapidly solidified AlSi17 alloy, the fine primary Si particles were homogenously distributed in the matrix. The experiments revealed that the microstructure of the AZ91/AlSi17 bonding zone was dependent on the microstructure of the inserts used. Applying an insert with coarse primary Si crystals led to the formation of a bonding zone composed of intermetallic phases and not fully reacted Si particles. The Si particles were too large to be consumed in the reaction with Mg during compound casting and fully transformed to Mg2Si. The use of an insert with a refined microstructure resulted in a bonding zone with fully reacted Si crystals. In this case, a eutectic (Mg17Al12 + a solid solution of Al in Mg) was observed in the bonding zone on the AZ91 side. The bonding zone close to AlSi17 alloy was composed of Mg2Si particles uniformly distributed in the Al-Mg intermetallic phase matrix.Keywords: Mg alloy, Al alloy, compound casting, intermetallic phases, bonding zone, microstructure
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