Fabrication of composite materials by mechanical alloying with cutting-chip of Al-Mg-Si alloy and fine Al2O3 powder.

Cutting chips of Al-Mg-Si alloy from manufacturing process of architectural products and submicron size Al2O3 particle are mechanically alloyed (MA) in a rotating ball mill, and extruded into a bar. Although without addition of Al2O3 particle, application of MA process to only Al-Mg-Si alloy cutting chips causes grain refinement in the extruded bar, and the tensile strength increases as high as 430 MPa. As increasing volume fraction( Vf. %) of Al2O3, both tensile strength and Young's modulus increase. The extruded bar of Al-Mg-Si alloy with 25 Vf. % Al2O3 after 24 hours milling exhibits the excellent value of 510 MPa in the tensile strength and 106 GPa in Young's modulus, respectively. Without addition of Al2O3, extruded bar shows more than 75 % of cold forgeability. As the content of Al2O3 powder increases, the cold forgeability decreases. The forgeability of extruded bar containing 20 Vf. % of Al2O3 particle is 25 %. Thermal expansion characteristics behaves the same way. Thermal expansion of the extruded bar of 25 Vf. % of Al2O3 is 1.83 x 10(-7) K-1 which is as low as stainless steel. Because of the introduction of grain boundary into crystal and dispersion of insulator particle, electric conductivity of the extruded bar contains 20 Vf. % of Al2O3 decreases to about 50 % of conventional Al-Mg-Si alloy.