高钙合金偏析理论研究与浇铸系统优化实践

本文首先对高钙合金钙元素偏析的行业难题进行了理论分析,通过单锭冷却模型及Pb-Ca二元合金相图发现降低冷却水的入水口水温使高钙合金快速冷却,来缩短L+Pb3Ca的存在时间,可达到抑止偏析的目的。其次对现有的浇铸系统进行研究,循环水槽内部铅隔墙的阻挡及冷却水出口流经使水温增加的主要因素。针对现有浇铸系统,采用"分割原理"进行优化设计,将2个大的循环水流系统,分割成为8个子循环水流系统,将水槽内部流通路径由3000mm缩短为600mm,缩短冷却水在模具内部的滞留时间,设计一定流程的露天水渠增加循环冷却时间。实践证明,优化设计后铸锭前后循环水槽进水温度由原来90℃降至40℃,水槽不同位点水温趋于恒定,高钙合金横截面内外侧偏析值为10ppm,满足行业要求。

Cu对Inconel 718合金Nb偏析影响机理的第一性原理研究

采用第一性原理计算与实验相结合的方法探究了Cu元素掺杂所造成的元素之间的交互作用对Inconel 718合金Nb偏析的影响。构建了掺杂前后Ni-Fe-Cr-Nb超晶胞模型,计算了掺杂前后各体系的形成热、结合能、态密度、差分电荷密度以及布居分布。计算结果表明,Cu原子的掺杂降低了体系的稳定性;掺杂改变了体系中元素之间的交互作用,影响了原子之间的键合强度及电荷密度分布,Cu的添加增加了基体中Fe原子和Cr原子之间的结合力,但同时也增加了Fe原子和Nb原子之间的排斥力。实验结果表明,微量Cu元素的加入降低了Fe和Cr的偏析,但促进了Nb元素的偏析。第一性原理计算和实验结果表明,Cu掺杂后Nb原子与周围Fe原子间排斥力的增加是Cu促进Nb偏析的本质原因。

Formation mechanism and criterion of linear segregation in ZL205A alloy

The experiments and numerical simulation were conducted for ZL205A aluminum alloy cylindrical shell casting. The formation mechanism of the linear segregation produced by the low pressure die casting (LPDC) process was investigated. And the heat transfer of the casting during solidification process was analyzed by simulation technique, resulting from the information of linear segregation obtained by plenty of experiments. The new linear segregation criterion was proposed through the simulation and experimental results. It was found that the melting metal with high Cu contents was feeding the crack shrinkage formed by the tearing under the effect of feeding pressure during the later solidification, which led to the formation of linear segregation. The control methods for the linear segregation were suggested based on the proposed mechanism. Finally, the criterion of linear segregation was confirmed by the production of the actual castings.