THE STRUCTURE AND PROPERTIES OF PRECIPITATION-STRENGTHENED COMPOSITES PRODUCED FROM A CAST ALLOY IN THE Al–Si–Mg SYSTEM

Abstract

The properties of precipitation-strengthened composites produced from an aluminum alloy were studied. The composites were prepared by powder and casting methods. The matrix was a water-atomized powder of the eutectic alloy in the ternary Al–Si–Mg system consisting of 2.9 wt.% Si, 6.9 wt.% Mg, and aluminum as the base component. The strengthening phase was a nanosized silicon carbide powder. The precipitation-strengthened composite was made employing the powder metallurgy method such as high-temperature extrusion of the powder mixture. The extruded rods that contained 4% SiC were used as a master alloy for the casting of the composite. This produced a cast precipitation-strengthened alloy with 0.5% SiC that combined high strength (to 220 MPa) and ductility at room temperature and demonstrated adequate high-temperature strength (to 120 MPa) at 300 °С. Increased content of the silicon carbide nanoparticles in the cast composite affected low-temperature properties because particles agglomerated on individual ingot areas. Symmetric and asymmetric rolling of the extruded semi-finished products resulted in high-strength composite ribbons showing a yield stress reaching 320 MPa and a tensile strength of 350 MPa. The contribution of different structural components to the total strength was analyzed and a conclusion was made that the proposed techniques should be implemented for making metal matrix powder composites. The use of powder rods containing 0.5% SiC as a casting master alloy allows the production of cast eutectic alloys that possess high strength and ductility and retain adequate high-temperature strength up to 300 °С.