Effects Of Melt Thermal Treatment And Modification On Microstructure And Property Of High Silicon Aluminum Alloy

High silicon aluminum alloys are widely used in machine, electron packaging and aerospace due to their properties such as light weight, high-strength, wear-resisting, heat-resisting and lower thermal expansion. However its properties depend on morphology, dimension and distribution of the primary Si and eutectic Si to a large extent. The effective method of obtaining inexpensive and high-performance is to modify and refine the primary Si and eutectic Si by added modifier in industry. When modification processes of high silicon aluminum alloy requried efficient and environmental, the trend was that developing a new master alloy including the comprehensive effects of refinement and modification. In this paper, based on the manufacture of AlTiCCe master alloy in preliminary experiments, it developed a new AlTiCCeP master alloy possessing of refinement and modification effects at the same time. Basing on preparation of the as-cast AlTiCCeP master alloy accompanying by the complex modification and metl thermal treatment, the effect of chemical modification, melt mixing and melt superheating on the the morphology, size and distribution of primary Si and eutectic Si of Al-20%Si was studied by OM, XRD, SEM and EDX. At the same time, the effect of morphology, size and distribution of the primary Si and eutectic Si of Al-20%Si on the hardness and wear resistance were discussed.The result of experiment showed that the AlTiCCeP master alloy was prepared by adding the sodium hexametaphosphate as phosphonium salts together with graphite and cerium oxide in the alumiunum melt holding 30 minutes, in which consisted of A1P、 TiC、TiAl3 and compound rare earth phase and possessed the well metamorphism and refinement effect on the high silicon aluminum alloy. As addition of 0.05% and 0.07% AlTiCCeP master alloy (as per phosphorus content), the size of primary Si of Al-20%Si and Al-30%Si were modified respectively by 30μm and 48 μm, which the eutectic Si changed from needle-like to point or short fibrous.The melt mixing result showed that mixing respectively the unmodified Al-20%Si at 900℃ and 580℃ refined the primary Si by less than 72 μm. When mixing the unmodified Al-10%Si at 580℃ and unmodified Al-30%Si at 900℃ according to mass tatio1:1, the primary Si of the mixed melt decreased by 37μm. The result of melt overheating showed that when superheating the Al-20%Si melt modified by AlTiCCeP master alloy to 900 ℃, the average size of primary Si could be further refined and below 26μm, which the eutectic Si changed into short fibrous. However the higher superheating temperature caused the serious oxidation of the aluminum melts and made oxides inclusions.The combination result of the melt thermal treatment and complex modification showed that mixing the Al-10%Si modified by AlTiCCe and the Al-30%Si modified by Cu-P to prepare the Al-20%Si, the average size of primary Si belowed 30μm. Then superheating the mixed Al-20%Si melt at 900℃, the average size of primary Si was further refined and the value was 10μm in which the eutectic Si changed from coarser needle-like to short fibrous.The experiment of wear resistance and hardness test showed that the hardness of Al-20%Si was increased as decrease of the size of primary Si. The friction coefficient and abrasion loss of Al-20%Si decreased as the decrease of the primary Si in dimension. The abrasion mechanism was primarily the oxidation wear together with some of adhesive wear.