【作者】 王峰；

【导师】 刘正；

【作者基本信息】 沈阳工业大学 ， 材料加工工程， 2010， 博士

【摘要】 为了满足汽车轻量化的需要,实现镁合金在汽车结构件上的应用,本文开展了复杂汽车结构件用压铸镁合金材料及压铸成形技术的研究。针对汽车转向器壳体对材料性能的要求,在AZ91合金的基础上,采用多元微量合金化的方法,通过添加Ca和Y元素,开发出了一种低成本高强韧压铸Mg-Al-Ca-Y合金,200℃时抗拉强度可以达到226.8MPa,比商用AZ91合金具有更好的室温力学性能和高温力学性能,可用于汽车上有特殊力学性能,特别是对高温性能要求的关键零部件的生产。根据细晶强化原则和稀土镁合金热处理强化的特点,采用冷模压铸工艺对不含铝的GWK系镁合金进行了研究,开发出高强度耐热压铸GWK系镁合金材料及压铸工艺,该合金经短时低温热处理后的力学性能能够进一步提高,其中GW123K-T4合金的室温抗拉强度、屈服强度和伸长率分别达到了269.4MPa、251.0MPa和4.2%。通过向GWK系合金中添加元素Ca和Zn,降低了稀土元素Gd的含量,不仅改善了合金的室温力学性能,而且降低了合金成本,这对压铸GWK系合金的应用具有重要的实际意义。根据汽车转向器壳体冲击试验条件,建立了壳体的有限元分析模型,利用有限元分析软件对镁合金转向器壳体结构进行了分析,并采用强度理论进行校核,为壳体材料替换的可行性提供理论依据。根据转向器壳体的技术要求,分析其结构及工艺性,并提出了铸件浇注系统的设计原则。利用理论计算及计算机数值模拟软件Flow3D对原铸件的浇注系统进行改进,并确定最佳的真空压铸排溢系统形式。利用慢压射理论,建立了压室内冲头慢压射运动的分析模型,利用Flow3D软件研究了压室内液态金属的运动规律,并得出最佳的慢压射工艺参数,即0.5m/s2匀加速运动。考虑到慢压射过程的影响,建立了带有压室填充的流体分析模型,并通过正交模拟试验研究真空压铸条件下镁合金转向器壳体的压铸充型过程,获得镁合金转向器壳体最佳的压铸工艺参数,即浇注温度为680℃,模具温度为200℃,压射速度3.4m/s(充型速度40m/s)。通过压铸试验验证模拟得到的工艺参数比较合理,在此工艺参数下采用AZ91-1.0Y-1.5Ca合金生产的铸件成形良好,并具良好的生产连续性及切削加工性,其力学性能优于原合金材料,产品合格率达到94%。镁合金转向器壳体的重量比铝合金转向器壳体的重量降低了33.5%,实现了产品的轻量化。采用真空压铸能够降低铸件中的气体含量,降低气孔尺寸且使其分布更加均匀,从而提高铸件的性能和合格率。通过对真空工艺参数的研究,得出最佳抽真空开启时间为0.8s,型腔真空度为5KPa时铸件质量最优。真空压铸镁合金壳体可以通过热处理来进一步提高其力学性能,经固溶与时效处理后,铸件可以获得更好的综合力学性能,其室温抗拉强度、屈服强度和伸长率分别达到280MPa、198.8MPa和5 %。与铸态合金性能相比,分别提高了12.5%,12.9%和2.0%。更多还原

【Abstract】 In order to fulfill demand of automotive lightweight and make application of automotive structural parts of magnesium alloys possible, new magnesium alloys for complex automotive parts and its corresponding high pressure die casitng(HPDC) technology were studied in the paper.According to the property demand of automotive steering gear housing, a new high strengthening and toughening Mg-Al-Ca-Y alloy with low cost was developed by using multi-alloying method, in which Ca and Y elements were added in the AZ91 alloy. With better mechanical properties at room and elevated temperature than those of commercial AZ91 alloy, the alloy can be used on parts with special mechanical properties demand, especially for key parts with demand of high temperature properties because ultimate tensile strength of alloy can reach 226.8MPa at 200℃. According to the principle of grain refinement strengthening and characteristics of RE-containing Mg alloy, a non-aluminum high strength and heat resistant die casting GWK(Mg-Gd-Y-Zr)magnesium alloy and corresponding cold mould die casting process as well as heat treatment process were developed. The mechanical properties of alloy can be enhanced by short time and low temperature heat treatment. The mechanical properties of die casting GW123K-T4 alloy can reachσb=269.4MPa,σs=251.0MPa,δ5=4.2%. In order to decrease the cost of GWK series alloys, adding Ca and Zn elements and reducing rare earth element Gd content may improve tensile mechanical properties of alloy at room temperature, which have extremely important practice significance to apply the GWK alloy.According to impact test conditions of steering gear housing, the finite element model of the steering gear housing was built and the structural analysis was performed using finite element analysis software and strength theory, which provided a theoretical basis for material substitution of steering gear housing. According to technological demand of steering gear housing, the structure and die casting process characters of die castings were analyzed. The improvement in pouring system of original castings and vacuum exhausting-flooding system was optimized and designed using theoretical calculation and Flow3D computer simulation software. Based on the theory of slow injection, analysis model of slow shot movement of shot plunger in shot sleeve was established. The movement rule of the liquid metal in shot sleeve and best slow shot parameters were investigated using Flow3D software. The optimal slow shot process was uniform acceleration motion with 0.5m/s2 acceleration rate. The fluid analysis model with sleeve filling was built considering influence of slow shot state. The best die casting processing parameters at vacuum condition were obtained using orthogonal simulation experiment as follow: pouring temperature 680℃, mold temperature 200℃and shot speed 3.4m/s(die filling speed 40 m/s).Experimental results of vacumm die casting showed that the optimal processing parameters by simulation were reasonable. Using the optimized processing parameters the AZ91-1.0Y-1.5Ca magnesium alloy castings were found good forming, good production continuity and cutting machining performance.The mechanical properties of magnesium alloy housing were better than those of the original alloy material, and product qualification rate can reach to 94%. The weight of magnesium alloy steering shell housing was decreased 33.5% compared with that of the aluminum steering gear housing, which realized lightweight of product.The vacuum die casting can reduce the gas content and gas porosity size, and make it more uniform distribution, thereby the mechanical properties and product qualification rate were increased. The optimal vacuum processing parameters were found as follow: vacuum starting time 0.8s and cavity vacuum pressure 5KPa. The mechanical properties of vacuum die casting magnesium alloy housing can be enhanced further after heat treatment. The best comprehensive mechanical properties of castings subjected to solid solution and aging treatment were obtained as follow: ultimate tensile strength 280MPa, yield tensile strength 198.8MPa and elongation rate 5%, compared with properties of as-die cast alloy, which increased by 12.5%, 12.9% and 2.0%, respectively.更多还原