高性能过共晶Al-Si-Cu-Mg合金组织与性能的研究

发布时间：2019-06-22 08:43

【摘要】：过共晶Al-Si-Cu-Mg合金具有比强度高、硬度高、线膨胀系数小、耐磨性好、热稳定性好等特点,是一种理想的汽车发动机活塞材料。常规的重力铸造过共晶Al-Si-Cu-Mg合金中粗大的初生Si和片层状的共晶Si对基体有割裂作用,影响合金的性能。因此改变共晶Si和初生Si的形貌进而提高合金性能成为国内外过共晶Al-Si-Cu-Mg合金在应用方面的研究重点。本文利用变质处理、合金化、挤压铸造和热处理等方法改善合金的显微组织,进而提高合金的力学性能。对过共晶Al-Si-Cu-Mg合金进行变质处理和合金化,研究变质处理和合金化对合金的显微组织及力学性能的影响。研究表明,Sr的加入使合金组织中的粗大片状共晶Si变为细小的纤维状,对挤压铸造合金进行变质处理时,随着P的加入原本挤压铸造时细小块状的初生Si反而长大,合金的抗拉强度及伸长率明显降低,主要是形成的Al-Sr-P影响了变质效果。Sr变质的挤压铸造合金的力学性能较好,抗拉强度为203.67MPa、伸长率为2.95%、硬度113.13HB。Ni、Cr和Mo的加入可以提高合金的力学性能,改善了过共晶Al-Si-Cu-Mg合金的显微组织,合金中的Al-Si-Mn-Fe多元相由花瓣状转变为粒状且弥散分布于基体中,阻碍位错的运动,对基体有一定的钉扎作用。合金化的合金的抗拉强度为231.50MPa、伸长率为2.86%、硬度124.10HB。挤压铸造选取了398MPa、598MPa、796MPa三个不同的挤压力。随着比压增加,初生Si相尺寸逐渐变小后逐渐消失;共晶Si相也得到明显细化,分布均匀,组织中α-Al枝晶明显增加,越来越发达。挤压铸造比压为598MPa时,力学性能最好,合金抗拉强度为231.50MPa,伸长率为2.68%,硬度为124.10HB。研究热处理对挤压铸造Al-17.5Si多元合金显微组织及力学性能的影响。分别改变固溶处理温度和固溶处理时间,Si相在尖端、凹槽处逐渐溶解、粒化,块状初生Si相逐渐细化,球化,棱角和尖端钝化,温度过高或时间过长时Si相出现粗化现象。同时热处理过程中析出的Al2Cu、AlNi相等也发生明显改变,多元合金相在热处理时发生消融现象,减小对基体的割裂作用,热处理对Al-Si-Cu-Mg摩擦磨损性能有较大影响,提高了合金的耐磨性。热处理1h和12h合金力学性能较好,抗拉强度达到274.5MPa和286.67MPa,硬度达到了130.63HB和144.07HB,伸长率达到4.00%和4.32%,且磨损量相近。
[Abstract]:Hypereutectic Al-Si-Cu-Mg alloy is an ideal piston material for automobile engine because of its high specific strength, high hardness, low linear expansion coefficient, good wear resistance and good thermal stability. The coarse primary Si and lamellar eutectic Si in the conventional gravity casting hypereutectic Al-Si-Cu-Mg alloy have cutting effect on the matrix and affect the properties of the alloy. Therefore, changing the morphology of eutectic Si and primary Si to improve the properties of hypereutectic Al-Si-Cu-Mg alloys at home and abroad has become the focus of application. In this paper, modification, alloying, squeeze casting and heat treatment are used to improve the microstructure of the alloy, and then the mechanical properties of the alloy are improved. The hypereutectic Al-Si-Cu-Mg alloy was modified and alloyed, and the effect of modification and alloying on the microstructure and mechanical properties of the alloy was studied. The results show that the coarse sheet eutectic Si in the microstructure of the alloy becomes fine fiber with the addition of Sr. When the squeeze casting alloy is modified, the primary Si of the fine block grows with the addition of P, and the tensile strength and extension of the alloy decrease obviously, mainly because the Al-Sr-P formed affects the modification effect. The mechanical properties of the squeeze casting alloy modified by Sr are better. The tensile strength is 203.67 MPA, the extension is 2.95%, and the hardness is 113.13 HB.Ni. the addition of Cr and Mo can improve the mechanical properties of the alloy and improve the microstructure of hypereutectic Al-Si-Cu-Mg alloy. The Al-Si-Mn-Fe multicomponent phase in the alloy changes from petal to grain and is dispersed in the matrix, which hinders the movement of dislocation and has a certain pinning effect on the matrix. The tensile strength, extension and hardness of the alloyed alloy are 231.50MPA, 2.86% and 124.10HB respectively. 398 MPA, 598 MPA and 796 MPA were selected for squeeze casting. With the increase of specific pressure, the size of primary Si phase gradually decreases and then disappears, the eutectic Si phase is also obviously refined and evenly distributed, and the 伪-Al dendrite in the microstructure increases obviously and becomes more and more developed. When the specific pressure of squeeze casting is 598MPa, the mechanical properties of the alloy are the best. The tensile strength of the alloy is 231.50 MPA, the elongation is 2.68%, and the hardness is 124.10 HB. The effect of heat treatment on microstructure and mechanical properties of squeeze casting Al-17.5Si multicomponent alloy was studied. When the solid solution treatment temperature and solid solution treatment time are changed respectively, the Si phase is gradually dissolved and granulated at the tip, the groove is gradually dissolved, the bulk primary Si phase is gradually refined, the spheroidizing, angular and tip passivation, and the coarsening of Si phase occurs when the temperature is too high or the time is too long. At the same time, the equality of Al2Cu,AlNi precipitated in the process of heat treatment also changed obviously, and the multicomponent alloy phase melted during heat treatment, which reduced the cutting effect on the matrix. Heat treatment had a great influence on the friction and wear properties of Al-Si-Cu-Mg, and improved the wear resistance of the alloy. The mechanical properties of the alloy are good at 1 h and 12 h after heat treatment, the tensile strength is up to 274.5MPa and 286.67 MPA, the hardness is up to 130.63HB and 144.07 HB, the elongation is 4.00% and 4.32%, and the wear rate is similar.
【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.21

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