A new procedure for blending die-cast Mg-Al alloys by semisolid processing to achieve controlled variations in microstructure and properties has been investigated. Granules of AM60B and AZ91D have been blended in varying proportions and Thixomolded at nominal solid fractions of 0.1 and 0.3, respectively. As-molded microstructures and the role of interdiffusion during processing have been analyzed in detail by scanning electron microscopy, transmission electron microscopy, and electron microprobe analysis. Tensile properties and failure modes have been analyzed and a strength model that considers solid solution strengthening of Al in the unmelted particles and a rule-of-mixtures behavior for microstructural components is proposed.