Influence of hydrogen content on the behavior of grain reflnement in hypereutectic aluminum-silicon alloy

Dissolved hydrogen is harmful to mechanical properties of refinedhypereutectic aluminum-silicon alloys. In the present work, by using a stepped-form mold and thehydrogen-detecting instrument HYSCAN II, the relationship between the initial hydrogen content inthe melt and the refinement effect on the casting of hypereutectic aluminum-silicon alloy wasinvestigated. The experimental results show that the cooling rate, the hydrogen content and thegrain refinement effect are three interactive factors. When the hydrogen content is above 0.20mL/100 g and the cooling rate is lower than that in 50 mm-thick step, hydrogen dissolved in thealloy melt influences the grain refinement effect. With increasing the cooling rate, the criticalhydrogen content increases too. It is expected that much hydrogen in the melt make the netinterfacial energy larger than or equal to zero, resulting in the shielding of the particles AlPduring solidification and that the critical gas content is closely related to the critical radius ofembryo bubbles.

Hydrogen Content and Porosity Behavior of Hypereutectic Aluminum-silicon Alloy with Phosphorus

By making castings that pick up gas from moisture in red sand molds,the porosity generated at different cooling rates was discussed during solidification of hypereutectic Al-25%Si alloy without and with phosphorus additions. The effect of phosphorus addition on hydrogen content in the melt was also studied. It was observed that the phosphorus addition made hydrogen content in alloy melts present a “see-saw' tendency.In addition to primary silicon refinement,the phosphorus promoted gas porosity formed not only in slowly cooled sections, but also in rapidly cooled sections. There was a small difference in density of full dense sample between P-refined and unrefined castings, with a larger density associated with phosphorous addition. The change of the surface tension seemed more reasonable to explain the mechanism of porosity behavior.

过共晶铝硅合金活塞的挤压铸造

采用挤压铸造的方法，作为尺寸较大的过共晶铝硅合金（含硅１６％～２０％）活塞的成型工艺．活塞毛坯的优质品率达到９５％以上．采用正交试验和极差分析法确定了挤压铸造的最佳工艺方案．试验证明，挤压铸造的主要工艺参数──单位压力，对活塞毛坯的外观质量和低倍组织有明显影响，而对合金的显微组织和机械性能的影响并不明显．经热处理后，活塞毛坯的机械性能指标达到或超过德国同类产品水平，并具有良好的切削加工性．

铸造工艺参数对Al-20％Si-Mg合金组织及性能的影响

研究了不同浇注温度、冷却强度对Al—20%Si—Mg合金组织及性能的影响。结果表明,浇注温度为750℃时,Al—20%Si—Mg合金组织中Mg_2Si和初晶硅晶粒均匀细小,硬度和耐磨性能较好;过低或过高的浇注温度均使材料中Mg_2Si和初晶硅晶粒变粗大,硬度和耐磨性能显著降低。同时,随着冷却强度的增加,材料的硬度和耐磨性能显著增强。