Effect of Mn on fracture toughness in Mg–6Al–1 wt.%Zn alloy

The effect of Mn content on fracture toughness and strength is investigated in Mg–6 wt.%Al–1 wt.%Zn alloy. As a result, the addition of 0.1–0.15 wt.% of manganese, which is close to the solubility limit of manganese is the most effective to avoid a significant reduction of fracture toughness and takes advantage of solution strengthening at the same time. The addition of Mn above the solubility resulted in the reduction of fracture toughness due to the formation of Mn-bearing particles. We defined the minimum size of void-nucleating particles and found that this minimum size increased with decreasing fracture toughness due to the formation of Mn–Al particles by the excessive manganese addition. In such a case, the reduction of the size of the second-phase particles is effective in improving the fracture toughness.