Fracture toughness of magnesium alloy AM60B

The fracture toughness of magnesium alloy AM60B was measured using 5-mm-thick compact tension specimens. Characterization of the fracture toughness behavior included tests in two different orientations and three temperatures. Scanning electron microscopy of fracture surfaces and metallography of surfaces parallel to the different orientations were performed to document the results. The fracture toughness tests indicated stable tearing behavior, and testing was discontinued when crack extension exceeded the clip gage capacity. Values of the Tearing Modulus and J(Q) were measured. These two parameters did not reveal any effect of specimen orientation on fracture toughness. Fracture surfaces on some of the tested compact tension specimens showed some porosity, which did not influence the fracture toughness values measured because the direction of crack-propagation was not influenced by the orientation of the porosity. Sub-size Charpy specimens were prepared in the same two orientations in which compact specimens were tested, as well as in other orientations in which compact tension specimens could not be prepared. Charpy impact testing also confirmed that the fracture toughness is generally independent of orientation effects. Force versus displacement traces from Charpy testing also confirmed the stable-tearing behavior observed in fracture toughness testing. Fracture toughness values would help designers choose from among the different materials if service-related experience indicates that better fracture toughness is desirable.