The results of investigations of the structure and mechanical properties of in-situ aluminum matrix composites based on the Al-Mg-Si system reinforced with primarily crystallizing silicides Mg2Si are presented. The main advantage of such materials is the usage of relatively inexpensive initial components with absence of the necessity for the use of powders, which greatly simplifies technology and reduces the production cost of castings. However, coarse morphology of primary crystals Mg2Si and needle structure of eutectic phase Mg2Si in cast composites have negative influence on the strength characteristics of obtained products. To control the morphology and size of endogenous Mg2Si particles, thermo-temporal treatment of the Al-Mg-Si melts has been tested. It was shown that the thermo-temporal treatment had a grain refining effect on the primary crystals of the Mg2Si reinforcing phase. With an increase in the duration of isothermal holding of the composite melt from 15 to 30 minutes at 900 °C, the average size of the reinforcing particles decreased substantially, and their total amount increased. A further increase in the holding time to 45 min led to coarsening of the morphology and growth of the inclusions, and upon holding for 60 min the amount of primary Mg2Si crystals decreased sharply and eutectic colonies were formed. Under the conditions of the experiments, the most favorable structural characteristics and mechanical properties of cast specimens were attained by isothermal holding of the melt at 900 °C for 30 min.Keywords: Al-Mg2Si in-situ composites, superheat melt treatment, microstructure, mechanical properties
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