アルミニウム鋳造の最新技術 ひずみ導入したＡｌ‐７％Ｓｉ‐０．５％Ｍｇ合金の半溶融凝固組織

Abstract

The effect of strain induced to alloys prior to the semi-solid processing (SSP) on microstructures was investigated on a Al–7%Si–5%Mg alloy. The microstructural changes during heating and isothermal holding at a semi-solid state were examined on a strain-induced alloy. The strain was induced by cold-rolling with a reduction ratio of 10 to 30%. The effect of cold-rolling on producing spherical and grain-refined α phase increases with increasing the reduction ratio up to approximately 20% and almost saturates at higher reduction ratio than 20%. During heating to 580°C, the characteristic boundaries become visible on the inside of the dendrite-shaped α phase. Simultaneously, the eutectic silicon particles are partially melted and the liquid phase preferentially flows into the small capillaries of boundaries. With increasing temperature the boundaries become more distinctive and act to break down the dendrites into small grains. The boundaries are considered to be formed as a result of recrystallization. The isothermal holding at 580°C of semi-solid temperature region for up to 600 s has essentially no eflfect to increase the size of the α phase and to change morphologies.