Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : October 07, 2017 - October 09, 2017
Although Mg alloy sheets are press-formed primarily by a warm forming method, room temperature forming is desired considering the hazards of machining magnesium, deterioration of the lubricants, and energy saving issues. In the deep drawing of the Mg alloy, because it’s the limit drawing ratio (LDR) was smaller at approximately 1.3, the deep drawability test cannot be evaluated using the n-value, r-value, or tensile strength, which are the typical parameters for evaluating the acceptability of the deep drawability. While deep drawing the AZ31 sheet, fracturing occurs not only at the break of the punch shoulder but also at the flange, depending on the molding conditions (F-type: 1.3<β<1.7, PF-type: 1.6<β<2.1, P-type: β>2.1). Fracture of the punch shoulder section is owing to the tension, and breakage of the flange part is regarded as breaking by compression. An in-plane compression jig for commercially available AZ31B-O Mg alloy was developed to observe the state when the fracture occurs, and an experiment was conducted. With this device, it was possible to provide compressive strain up to -0.15 in a state where the out-of-plane buckling was suppressed to the sheet. As a result of the experiments, the rupture stresses obtained were: a tensile rupture stress of 252 MPa, an out-of-plane shear breaking stress of 401 MPa, and an in-plane shear breaking stress of 544 MPa. In order to induce the in-plane shear fracture observed at the flange portion, the magnitude of stress required is 2.16 times as high compared to the stress required for the tensile fracture of the punch shoulder portion. Therefore, it is reasonable to assume that the fracture of the flange portion occurs as the starting point of the tensile fracture of the punch shoulder portion, which progresses to the flange portion and undergoes in-plane shear fracture.
