Forsmark, J., Dowling, Z., Gibson, K., Mueller, C. et al., "An Investigation of the Effects of Cast Skin on the Mechanical Properties of an AM60 Die-Cast Magnesium Alloy," SAE Int. J. Mater. Manf. 8(3):714-721, 2015, doi:10.4271/2015-01-0510.
Magnesium die-cast alloys are known to have a layered microstructure composed of: (1) An outer skin layer characterized by a refined microstructure that is relatively defect-free; and (2) A “core” (interior) layer with a coarser microstructure having a higher concentration of features such as porosity and externally solidified grains (ESGs). Because of the difference in microstructural features, it has been long suggested that removal of the surface layer by machining could result in reduced mechanical properties in tested tensile samples.To examine the influence of the skin layer on the mechanical properties, a series of round tensile bars of varying diameters were die-cast in a specially-designed mold using the AM60 Mg alloy. A select number of the samples were machined to different final diameters. Subsequently, all of the samples (as-cast as well as machined) were tested in tension. This paper will present the results of this study and detail some of the issues that influence the tensile behavior in the die-cast AM60 alloy.