Effects of layer thickness ratio on the bendability of Mg-Al-Zn/Mg-Gd laminated composite sheet

Despite the laminated composite sheets of dissimilar magnesium (Mg) alloys have attracted great attention due to their excellent comprehensive mechanical properties as compared to the sheets of individual alloys, how the structural parameters, especially the layer thickness ratio (LTR), influence their formability is still left unstated in the previous researches. We investigate the effects of LTR on the bendability of the co-extruded laminated composite sheet of Mg alloys, Mg-Al-Zn/Mg-Gd, by combining the V-shaped bending experiments, quasi-in-situ electron backscattered diffraction (EBSD) measurement and finite element (FE) simulations. When the layer Mg-Gd is placed in the outer layer, the bendability of the laminated composite sheet first increases and then decreases, and it reaches the optimum at an LTR (AZ31:Mg-Gd) of 2:1, which goes against the intuition that the higher the volume fraction of the Mg-Gd alloy, the better the bendability. This phenomenon is explained by the competitive effect between the improved plasticity of the outer layer and the enhanced tensive-compressive asymmetry of the outer and inner layers with increasing the thickness of layer Mg-Gd. The neutral layer migrates from the geometrical central layer to the compressive zone due to the asymmetrical responses of the inner and outer layers. Both the shift of the neutral layer and the strain of the outer layer increased by reducing the LTR. It is believed that this research provides some new insights into the design and development of high-formability laminated composite sheets of Mg alloys.