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Al-Mg alloys were fabricated by hot extrusion process after vacuum + argon-protected casting. The effects of Sc microalloying on microstructure and properties of as-extruded Al-5Mg alloy were studied. The results show that alloy 2 containing Sc is partially recrystallized during hot extrusion, resulting in the structure of alloy 2 consisting of 21.8% equiaxed recrystallized structure and 78.2% fine banding structure. The grain size of alloy 2 is about 5.31 μm, which is 83.3% finer than that of alloy 1 without Sc. The sum of the yield strength increments due to grain boundary strengthening (σGB) in alloy 2 is 103.59 MPa, where low angle grain boundary strengthening (σLAGB) is increased by a factor of 4.5, and high angle grain boundary strengthening (σHAGB) is increased by 73.4% compared to that of alloy 1. The addition of 0.2% Sc leads to an increase in the lattice strain and dislocation density of alloy 2, and the dislocation strength (σdis) increases to 41.85 MPa. The alloy 2 with Sc has a higher tensile strength of 380.7 MPa, which is 34.1% higher than that of alloy 1, but alloy 2 has a 46.2% reduction in elongation compared to alloy 1.

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