【作者】 刘艳华；

【导师】 杨湘杰；

【作者基本信息】 南昌大学 ， 材料物理与化学， 2007， 硕士

【摘要】 液态压铸件内部缺陷率较高，产品不能热处理，力学性能较低。因此如何降低压铸件的缺陷率，提高铸件力学性能成为急需解决的问题，并引起广大研究学者的关注。以江西江铃有色金属压铸厂要求达到的力学性能指标为目的，本文以A380铸造铝合金试杆为例，利用实验室自主开发的剪切低温浇注式流变制浆工艺(Low Superheat Pouring with a Shear Field，简称LSPSF)制备半固态浆料，结合DCC280型号卧式压铸机系统研究了半固态流变压铸成型工艺。主要研究了LSPSF法制备A380铝合金半固态浆料最佳工艺参数优化、液态压铸和半固态压铸工艺及其铸件显微组织与力学性能、液态压铸和半固态压铸热处理工艺及其铸件显微组织与力学性能。并进行了流变压铸工艺参数对铸件质量的影响分析。试验结果表明：(1)LSPSF法制备A380铝合金的最佳工艺参数为：①浇注温度620℃；②输送管转速90rev／min；③结晶器预热温度550℃；④倾斜角度25°。浇注温度和输送管转速共同影响着输送管对合金熔体的激冷和搅拌混合强度，只要浇注温度和输送管转速能够良好匹配，使出口温度低于合金液相线温度，便可以获得优质的半固态浆料。(2)在LSPSF工艺中，低过热浇注、凝固初期的激冷和搅拌混合可有效的激发熔体形核，促进晶粒游离，提高游离晶的存活率，这也是半固态组织细化的本质所在。(3)力学性能测试表明，两种不同成形方法所得成形件在压铸态时强度相差无几，但半固态成形件的塑性几乎是液态成形件的2倍。经过同样的T6热处理后，半固态压铸件的抗拉强度有所提高，液态压铸件的抗拉强度却下降很大。伸长率均有所下降，但两者变化的幅度不同，液态压铸件的延伸率下降更多。(4)试验过程需要严格控制压铸工艺参数及合金熔炼工艺，否则即使在半固态流变压铸条件下，也会因缺陷的产生而导致力学性能的下降。然而与同等条件下的液态压铸件相比，这些缺陷明显要小得多。总体来看，半固态流变压铸实验结果仍较好于液态压铸，且随着浇注温度的降低，压铸缺陷的减少，得到的组织越趋于圆整、细小，力学性能越高。更多还原

【Abstract】 Traditional die-casting internal defect ratios are always high, and can not easily do the heat treatment, so how to reduce these defect ratios is an emergent question which needs to be solved has already gathered much concern of scholars.In order to improve the mechanical properties for Jiang ling die-casting corporation, the paper systematically does some research on semi-solid rheological forming technology mainly on testing bar which is made of A380 aluminum casting alloy.And the study uses a novel rheocasting process ,termed as Low Superheat Pouring with a Shear Field(LSPSF) to prepare semi-solid slurry, the forming equipment is die-casting machine(DCC280). The paper include three parts:the optimization of the LSPSF technical parameters. the microstructure and mechanical properties of liquid die-casting parts and semi-solid die-casting parts before and after heat treatment, then does analysis and research on the influence of rheological die-casting technical parameters to the performance of castings. Research method and main results is as following:(1) we received the best microstructure of the A3 80 semisolid aluminum slurry when the rotating speed is 90rev/min , pouring temperature is 620℃, inclined degree is 25°and the temperature of the crucible is 550℃. Pouring temperature and rotation speed of barrel determine the stirring-mixing intensity and cooling ability applied by the rotational barrel on the molten alloy. It can be concluded that sound semi-solid metal slurry can be produced under the appreciate combination of pouring temperature and rotation speed of barrel.(2) Under LSPSF process, low superheat pouring combined with localized rapid cooling and vigorous mixing during the initial stage of solidification can enhance wall nucleation, crystal separation and crystal survival. Moreover the effective nucleation rate is significantly affected by the combined effects of pouring temperature and rotation speed of barrel.(3) Mechanical property test shows that semi-solid die-casting and liquid die-casting have almost the same tensile strength before they are heat treatmented. but the ductility of the semi-solid forming parts is almost two times than that of liquid forming parts. After T6 heat treatment, the tensile strength improved and the ductility inclined for both semi-solid die-casting and liquid die-casting , but they have different variation range.(4) The result shows that these parameters should be strictly controlled or the mechanical properties will fall down because of the defects producing, though under semi-solid rheological die-casting. However, the results of semi-solid one is better than the traditional one, accompanied with descending of pouring point and reducing of detects, finally gains more near-circular and smaller structures.the mechnical properties more improved.更多还原