Tensile coherency in semi-solid AZ91 alloy

Hot tearing during casting is related to tensile loads arising in the semi-solid region during solidification. The tensile strength of AZ91 in the semi-solid region was therefore investigated. Results indicate that the tensile strength of the mush at high fraction solid is due to the strength of the bonded solid grains while at low fraction solid the tensile strength is related to the surface tension of the liquid film between the grains. In the case of equiaxed AZ91, this transition in the bonding mechanism occurs at 85% solid.