Improvement of mechanical properties of in situ Mg-Si composites via Cu addition and hot working

The synergistic effects of copper addition and hot extrusion process on the modification of microstructure and enhancement of mechanical properties of a common in situ hypereutectic Mg-Si metal-matrix composite were studied. It was revealed that Cu addition at the microalloying level of 0.5 wt% was very effective in modifying the primary and eutectic Mg2Si phases, which led to the enhancement of the as-cast mechanical properties. Further Cu additions (2, 4.5, 8, and 15 wt%) led to the appearance of the '-Mg/Mg2Cu eutectic constituent and distinct '-Mg regions with the disappearance of Mg2Si eutectics in the ingots, which was ascribed to the change in the solidification path. Contrary to the favorable effect of Cu at the micro-addition level, higher additions led to poor tensile properties due to the deleterious effect of eutectics. Fragmentation and dispersion of intermetallics, as well as intense grain refinement by dynamic recrystallization (DRX) were observed for the extruded composites due to the hot deformation effects, which resulted in the enhancement of the ultimate tensile strength, total elongation, and tensile toughness. Accordingly, it was concluded that Cu addition to Mg-Si composites should be limited to small amounts for modification effects, and if it is combined with the elevated-temperature thermomechanical processing, the optimum strength-ductility trade-off can be achieved. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

The synergistic effects of copper addition and hot extrusion process were studied on the modification of microstructure and enhancement of mechanical properties of a common in situ hypereutectic Mg-Si metal-matrix composite. The results showed that copper addition at a microalloying level of 0.5 wt% effectively modified the microstructure and improved the mechanical properties of the as-cast material. However, higher copper additions led to poor tensile properties due to the deleterious effects of eutectics. The hot extrusion process resulted in fragmentation and dispersion of intermetallics, as well as intense grain refinement by dynamic recrystallization, leading to enhanced mechanical properties of the composites.