Study on Interface Microstructures and Mechanical Properties of Laminated Mg-Al Sheets

Abstract

In this study, the influence of thermo-mechanical treatment on the interface microstructural evolution and subsequent mechanical properties of a roll-bonded Mg-Al 2-ply clad sheet was investigated. After warm roll bonding process, post-heat treatment is typically needed for relaxing a high dislocation density in constituent alloys. It is hard to avoid the generation of IMC layers at Mg/Al interface during general annealing treatment. Intermetallic compound (IMC) phases, γ (Mg17Al12) and β (Mg2Al3) were generated at the interface between the constituent Mg and Al alloys. The thickness of the IMC layers increased to more than 10 μm with increasing annealing time up to 3 h at 300 ºC. Upon extending the annealing time to 12 h, the β phase at the interface between Al and Mg hardened significantly. The thickness of IMC layers, grew sufficiently during annealing treatment, was however reduced due to grain refinement effect. Especially, the thickness of γ (Mg17Al12) layer is dramatically decrease compared to the thickness reduction of β (Mg2Al3) layer in secondary rolling process at 300 ºC. The local mechanical properties of the γ and β phases were investigated by using nanoindentation. Furthermore, the mechanical properties of the two constituent alloys and the 2-ply clad sheets were systematically investigated by uniaxial tensile test. Taking both tensile strength and elongation into account, the 2-ply sample annealed for 10 min at 300 ºC exhibited acceptable overall mechanical properties. The mechanism for initiation of interfacial delamination in the direction parallel to the tensile loading direction was confirmed by observation from the thickness surfaces of the tensile specimens using digital image correlation (DIC). Abrupt crack initiation was observed at Mg/Al interface, followed by the generation of stress concentration in the sample annealed for 30 min and 60 min, indicating that the overannealing-induced brittleness of a specific IMC phase at the interface may be detrimental to overall mechanical properties of the roll-bonded 2-ply clad sheet adopted in this study.