材料期刊网

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.

The effects of ultrasonic treatment (UT) and electromagnetic stirring (EMS) forces, individually and in combination, prior to high pressure die-casting of AA5754 alloy were assessed. The liquid of alloy was subjected to UT, EMS and the combined style and then transferred to the shot chamber. The grain size, mechanical properties, gas content and hot tearing susceptibility were analyzed. The results suggest that the application of each process enhances grain refinement and decreases the porosity of the specimens. UT reduces the grain size from 140 to 82 μm and decreases the porosity from 5.5% to 1.4%. EMS reduces the grain size to 107 μm and the porosity to 3.3%. The combination of UT and EMS decreases the grain size and the porosity to 65 μm and 1.1%, respectively, which are the lowest grain size and porosity ever reported for this alloy achieved via physical processing. Intensive cavitation and stirring not only resulted in a refined microstructure but also significantly decreased the hot tearing susceptibility and improved the mechanical properties. All of the aforementioned characteristics are due to cavity formation, during each process. By combination of techniques, EMS could promote the nucleation process by providing more exogenous particles in the strong cavitation field of UT. Ultrasonic plays a major role in grain refining, decreasing the hot tearing susceptibility and the gas content by introducing a strong cavitation field.