The roles of La content on the microstructure, corrosion resistance and discharge behavior of as-extruded Mg–6Al–3Pb alloy bars: Actual experiments and first-principles calculations

The microstructure, corrosion resistance and discharge properties of as-extruded Mg–6Al–3Pb- x La ( x = 0.5, 1.0 wt%) alloy bars in the transverse direction (TD) and extrusion direction (ED) were systemically investigated and compared. With the increase of La content, the second phase (mainly Al 11 La 3 , LaAl 3 ) was gradually increased from 3.69 % to 4.19 %–6.82 % and 5.59 %. However, their average grain size was similar, from 24.42 μm to 25.66 μm–21.31 μm and 23.05 μm. The microstructure was different between the different directions (ED or TD), (1) the distribution characteristic of second phase: The second phase was uniformly distributed in the TD-samples, whereas the counterparts in the ED-samples were irregularly distributed in bands, predominantly along the ED. (2) the distribution characteristic of texture: the color of grains in the TD-samples was blue or green (mainly composed of non-basal plane orientations.), whereas the counterparts in the ED-samples were red or purple (The basal plane orientation is predominant). Regarding corrosion behaviors, the AP63-1La alloy presented the better corrosion resistance compared to the AP63-0.5La alloy, mainly be ascribed to the increased volume fraction of Al 11 La 3 and LaAl 3 phase. The essence was that both of them had higher potentials/better corrosion resistance than the Mg-matrix, which was verified by the calculation of work function (Al 11 La 3 : 4.18, LaAl 3 : 4.49, Mg: 3.70) via DFT calculation. In terms of discharge properties, the AP63-1La (TD) alloy had the best discharge properties with an average discharge potential of −1.707 V (vs. SCE).