Precipitation behavior during homogenization of direct chill cast aluminum alloy 1100.

The precipitation behavior during homogenization of DC cast aluminum alloy 1100 has been invesigated by means of electrical resistivity measurement and transmission electron microscopy. Precipitation is accelerated above 300°C and small AlFeSi precipitates (mainly of α-AlFeSi) are observed around 450°C, when ingot is heated up at a rate of 50°C/hr. The precipitates grow and disperse in matrix along with dissolution of α-AlFeSi, precipitation of Al3Fe and probable transformation from α to Al3Fe, when heated above 500°C or held at each temperature. Al3Fe also precipitates at the interface between crystallized intermetallic compound and matrix above 550°C, and no precipitates exist in the matrix after prolonged holding at 600°C. In case where the ingot is cooled down at 20°C/hr and held after homogenization at 550°C the 3hr, precipitation progresses with almost constant distribution in matrix. The precipitates appear in matrix at lower temperature around 400°C and after prolonged holding below 500°C, when the ingots are cooled after heating at 600°C for 9hr.