局部加压铝合金的成分偏析及其形成机理的研究

Segregation and Its Mechanism of Al Alloys by Local Pressurization

实验研究两种不同凝固特性的铝合金在局部加压工艺下的成分偏析现象。采用ICP法分析不同位置元素Cu的含量,结果表明:糊状凝固特性的合金AC4B易在加压杆下方15mm处形成较严重的负偏析,离加压杆越远,偏析越轻。层状凝固特性的ADC12仅在加压杆圆柱面下方5mm处有轻微的负偏析,同时加压杆圆柱面周围则形成了正偏析。AC4B中加压开始时间较早或较晚时,产生的偏析较轻。而ADC12中偏析程度几乎不受加压开始时间的影响。偏析的生成是因为局部加压使枝晶间的残余金属液产生局部流动而形成的。

A study for local pressurization was carried out to examine segregation occurred in two kinds of Al alloys having different solidification modes. The results of copper content analyzed by ICP illustrate that segregation under the pressurization pin tip is negative one and easily occurred for AC4B rather than for ADC12 alloy. The degree of segregation differs with position from the pin tip in the casting in AC4B casting. Negative segregation in ADC12 casting only occurred in annular position about 5 mm below the pin tip. On the contrary, there appears positive segregation of copper in the upper zone around pin. Segregation is affected by pressurization timing for AC4B rather than ADC12 casting. Segregation is caused by remained metal liquid, which is driven by local pressure.