论文部分内容阅读
在高压模铸AA5754合金前,分别采用超声处理和电磁搅拌或两者组合使用对熔体进行处理,并对其影响进行评定。经超声处理、电磁搅拌或组合处理后的合金熔体被转移至注射腔。对合金的晶粒尺寸、力学性能、含气量和热裂敏感性进行分析。结果表明,各种熔体处理方法都能使合金的晶粒细化,孔隙率减小。超声处理使合金晶粒从140μm减小至82μm,孔隙率从5.5%减小至1.4%。电磁搅拌使合金晶粒减小至107μm,孔隙率减小至3.3%。组合处理使合金晶粒和孔隙率降至该合金采用物理熔体处理方法有报道以来的最低值,分别为65μm和1.1%。强烈的空化效应和搅拌不仅可以得到细化的显微组织,而且也减小热裂敏感性,提高力学性能。以上特征都是由于在熔体处理过程中产生空洞。通过组合处理,电磁搅拌在强烈的超声空化场中提供更多外生颗粒以促进形核。超声处理通过引入强烈的空化场,在晶粒细化、减小热裂敏感性和含气量过程中起主要作用。
Prior to the high pressure die casting of AA5754 alloy, the melt was treated with sonication and electromagnetic stirring, or a combination of the two, respectively, and their impact assessed. The alloy melt after sonication, electromagnetic stirring or combined treatment is transferred to the injection chamber. The grain size, mechanical properties, gas content and thermal susceptibility of the alloy were analyzed. The results show that all kinds of melt processing methods can make the alloy grain refinement, porosity decreases. Sonication reduced the alloy grains from 140 μm to 82 μm and the porosity decreased from 5.5% to 1.4%. Electromagnetic stirring reduced the alloy grains to 107μm and the porosity decreased to 3.3%. The combined treatment reduced the alloy grain and porosity to the lowest values reported for the alloy by physical melt treatment, at 65 μm and 1.1%, respectively. Strong cavitation effect and stirring can not only get refined microstructure, but also reduce the thermal cracking sensitivity and improve the mechanical properties. The above features are all due to voids in the melt processing. Through the combination process, electromagnetic stirring provides more exogenous particles in the intense ultrasonic cavitation field to promote nucleation. Ultrasonic treatment through the introduction of a strong cavitation field, in the grain refinement, reduce the susceptibility to hot cracking and gas content plays a major role.