Influence of Lanthanum Addition on Microstructural and Mechanical Properties of Magnesium-Aluminium-Lithium-lanthanum Alloy

Effect of Lanthanum addition on mechanical properties of LA93 along with its microstructural evolution has been analysed using optical microscopy, scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The phases of this alloy were identified by X-ray diffraction (XRD). La addition has resulted in a reformed semi continuous structure with a decrease in grain volume along the boundary. The morphology shows the formation of Al₂La and Al₃La phase while the AlLi in LA93 has decreased. At 1.5 wt% La addition, the maximum grain refinement is obtained. In LA93+xLa, the Al₂La and Al₃La appear as a white long stripy phase and a white large blocky phase, respectively, and contribute to the increased strength of the alloy. There is a clear distribution of intermetallic compounds along the grain boundary of α-Mg and inside the matrix. The ultimate tensile strength increases by 60% to 112 MPa and hardness increases by 48% when the La content is 1.5 wt%. This improvement can be attributed to the precipitation of intermetallic compounds and grain refinement of β-phase which impede the dislocation motion. The elongation also increased considerably with the lanthanum addition.