【摘要】 研究了 70 75铝合金在液相线及液相线温度附近等温形核过程和组织变化情况·在液相线温度以上 (6 4 5℃ ) ,熔体激冷形核数量相对较少 ,晶粒较大 ,单位面积晶粒数较少且基本不随保温时间变化 ;在逼近液相线温度 (6 32℃ ) ,熔体大量形核 ,晶粒细小球化 ,单位面积晶粒数较多 ,随保温时间先增加后减少 ,在 30min左右达到最大值 ;在液相线温度以下 (6 15℃ ) ,熔体形核数量多 ,但部分合并长大 ,细小的晶粒中伴随着一些粗大晶粒 ,单位面积晶粒数较少 ,随保温时间先增加后减少 ,在 30min左右达到最大值·结果表明 ,在逼近液相线温度 (6 32℃ )下形核保温 30min铸造可期望获得优良的半固态浆料·更多还原

【Abstract】 The nucleation procedure and chilling structures were studied when 7075 alloy was held in liquidus temperature or near it. In the temperature above liquidus (645?℃),the melt has a little nucleation. The grains are big. The number of grains per area is small and is stable with the variation of the holding time. In the temperature near liquidus(632?℃), there are lots of nucleation in the melt. The grains are fine. The number of grains per area is bigger and first increases, then decreases with the holding time. The optimum time is about 30?min. In the temperature below liquidus (615?℃), the nucleation number is the biggest, but some nucleuses congregate and grow largely. The number of grains per area is small and first increases, then decreases with the holding time. The optimum time is also about 30?min. The results show that fine semisolid slurry of 7075 aluminium alloy is expected to be obtained by liquidus casting when the melted alloy is held about 30?min closely near liquidus.更多还原