【摘要】 采用热分析技术与组织观察研究了混合稀土(MM)加入对Sr变质Al-13%Si合金共晶凝固的影响。研究发现:少量MM(0.2%)加入导致Sr变质合金的显著形核温度(TN)、再辉前最低温度(TM)和共晶生长温度(TG)显著降低,进一步增加MM(0.5%,1.0%)加入量反而使得这些特征温度升高,与仅Sr变质合金的相近;当MM加入量为0.2%时,因共晶Si相在更低温度下生长,导致共晶Si相的进一步细化。大量MM加入后,共晶体在相对较高的温度下生长而导致共晶Si相的粗化。在Sr变质合金中加入少量的MM进一步消除了潜在的共晶体的形核基底,因而使TN值大大降低,但凝固模式并未发生显著的改变。大量MM的加入可能使得合金液中共晶体的外来形核核心数量激增,因而TN反而升高,在试样中部区域也出现了共晶体的大量独立形核区,显著改变了共晶凝固模式。更多还原

【Abstract】 Thermal analysis and micro/macro-structure observation were employed to investigate the effect of addition of misch metal(MM)on eutectic solidification of Al-13%Si alloy modified with strontium. It was found that small amount of MM addition(0.2%)would result in a considerable decrease in characteristic temperatures, TN(noticeable eutectic-nucleation temperature), TM(the lowest temperature prior to recalescence)and TG(the eutectic growth temperature), during cooling of alloy melt, and with further increase in addition amount of MM, these temperatures on the contrary would increase, closed to that of only Sr-modified alloy. When addition amount of MM was 0.2%, the remarkable decrease of TG caused a further refinement of eutectic Si, while, with more addition of MM(0.5%, 1.0%), the rise in TG led to coarsening of eutectic Si. Thermal analysis and macrostructure observation indicated that small amount of MM addition in Sr-modified Al-13%Si alloy further removed the heterogeneous sites for eutectic nucleation, and hence resulted in the considerable reduction of TN, therefore the eutectic solidification mode was not altered. However, more addition of MM was thought to introduce some new heterogeneous nucleation sites, and thus TN was raised up again and independent eutectic nucleation behavior was observed in the inner part of castings, so the eutectic solidification mode was obviously changed.更多还原