挤压铸造过共晶Al-Si合金组织与性能研究

发布时间：2018-04-28 00:39

本文选题：过共晶Al-Si合金 + 挤压铸造　；参考：《沈阳工业大学》2017年博士论文

【摘要】：过共晶Al-Si合金具有硬度高、耐磨性好、线膨胀系数小、密度低等优点,是理想的汽车用活塞材料。但常规方法制备的过共晶Al-Si合金组织中粗大块状的初生Si相和针片状的共晶Si相严重影响合金的综合力学性能,因此改善初生Si及共晶Si的尺寸、形貌与分布,成为国内外过共晶Al-Si合金应用研究的重点。本文通过挤压铸造成形工艺改善过共晶Al-Si合金的显微组织,从而强化合金,提高其力学性能。挤压铸造可显著提高Al-17.5Si二元合金的力学性能。随着挤压铸造比压的增加,合金的硬度、抗拉强度和伸长率均得到大幅度提高,当挤压铸造比压为600MPa时,合金综合力学性能取得最佳值。挤压铸造过共晶Al-Si合金中各相的形貌与分布均得到了明显改善,粗大初生Si相数量减少,α-Al枝晶析出,共晶组织显著细化。将Sr变质后的Al-17.5Si二元合金在压力下凝固,合金中共晶Si相进一步细化,变为十分细小的纤维状。而当对合金进行P变质后挤压铸造成形,合金组织中则出现了大量粗大的初生Si颗粒,使得合金的抗拉强度和伸长率出现了减低的趋势。由此确定,Sr变质处理适用于挤压铸造过共晶Al-Si合金。挤压铸造使A390和LM280合金的组织发生明显变化,组织中不仅出现α-Al枝晶,初生Si数量减少,共晶组织更加致密,而且Al2Cu相、Mg2Si相、Al7Cu4Ni和Al1.9Cu1.0Mg4.2Si3.3等第二相尺寸的逐渐变小,且数量减少,合金元素在基体中的固溶度提高。挤压铸造提高了多元过共晶Al-Si合金的力学性能,当挤压铸造比压为600MPa时,合金的硬度和强度达到峰值。挤压铸造可显著改善Al-(15,17.5,22)Si合金的显微组织,合金的力学性能明显提高,磨损量显著降低,合金的耐磨性能得到有效提高。且随着Si含量的增加,合金的磨损量进一步下降,耐磨性能提高。在均匀化退火过程中,挤压铸造过共晶Al-Si合金中的Si相经历了熔断、粒化和粗化的过程,形貌越来越圆整,分布趋于均匀。均匀化退火后挤压铸造过共晶Al-Si合金的力学性能与耐磨性能都得到了改善,这主要可归结于Si相形貌、尺寸及分布的改善,在525oC均匀化退火8~12h时,Si相颗粒细小(等效圆直径为2.0~2.5μm)、园整、分布均匀,合金的综合力学性能和耐磨性能达到最佳。挤压铸造过共晶Al-Si合金坯锭经热挤压后组织发生显著变化,发达的α-Al枝晶基本消失,细小珊瑚状的共晶Si相破碎为小粒状,平均尺寸2~4μm,这些细小的Si相颗粒弥散分布在合金基体中,从而获得了细小Si相硬质颗粒弥散均匀分布于软质Al基体的均匀组织,最大程度地发挥了合金的潜能。对挤压铸造Al-17.5Si二元合金坯锭进行热挤压成形,可大幅度提高合金性能,尤其使合金的塑性有了显著的改善。对挤压铸造过共晶Al-Si合金进行了热模拟实验,发现挤压铸造过共晶Al-Si合金在相同变形条件下应力水平较重力铸造合金略高,其合金热变形激活能为308.77kJ/mol,结合热加工图得到挤压铸造合金的合理热加工参数为:变形温度450oC~500oC,应变速率0.01s~(-1)~0.1s~(-1)。在该条件下对合金进行热挤压,抗拉强度达到了332.1MPa,较重力铸造提高了135%,伸长率为13.51%,较重力铸造提高了923.5%。
[Abstract]:Hypereutectic Al-Si alloy has the advantages of high hardness, good wear resistance, low coefficient of linear expansion and low density, and it is an ideal piston material for automobile. However, the coarse bulk Si phase and needle like eutectic Si phase in the hypereutectic Al-Si alloy prepared by conventional methods seriously affect the comprehensive mechanical properties of the alloy. Therefore, the primary Si and eutectic Si are improved. The size, morphology and distribution of the hypereutectic Al-Si alloy at home and abroad are the focus of application research. In this paper, the microstructure of Hypereutectic Al-Si alloy was improved by squeezing casting process, thus strengthening the alloy and improving the mechanical properties of the alloy. The mechanical properties of Al-17.5Si two yuan alloy can be greatly improved by extrusion casting. With the increase of compression casting specific pressure The hardness, tensile strength and elongation of the alloy have been greatly improved. When the compression casting specific pressure is 600MPa, the overall mechanical properties of the alloy obtain the best value. The morphology and distribution of each phase in the hypereutectic Al-Si alloy of squeezed casting have been obviously improved, the number of coarse primary Si phase decreases, the -Al dendrite precipitates and the eutectic microstructure is remarkably refined. The Al-17.5Si two element alloy after Sr metamorphism solidifies under pressure, and the eutectic Si phase of the alloy is further refined and becomes very small fiber. And when the alloy is modified by P after the extrusion casting, a large number of coarse primary Si particles appear in the alloy structure, which makes the tensile strength and elongation of the alloy decrease. It is determined that Sr modification is suitable for extrusion casting hypereutectic Al-Si alloy. Extrusion casting makes the microstructure of A390 and LM280 alloy change obviously. The microstructure of the microstructure appears not only a -Al dendrite, but also the number of primary Si, the eutectic microstructure is more compact, and the second phase size of Al2Cu phase, Mg2Si phase, Al7Cu4Ni and Al1.9Cu1.0Mg4.2Si3.3 gradually becomes smaller, and the size of the second phase of Al2Cu phase, Al7Cu4Ni and Al1.9Cu1.0Mg4.2Si3.3 becomes smaller gradually, and the phase of the second phase of Al2Cu phase, Al7Cu4Ni and Al1.9Cu1.0Mg4.2Si3.3 becomes smaller and smaller gradually. As the amount is reduced, the solid solubility of alloy elements in the matrix is improved. Extrusion casting improves the mechanical properties of polyeutectic Al-Si alloy. When the compression casting ratio is 600MPa, the hardness and strength of the alloy reach the peak value. The microstructure of Al- (15,17.5,22) Si alloy can be greatly improved by extrusion casting, and the mechanical properties of the alloy are obviously improved and the wear amount of the alloy is obviously improved. The wear resistance of the alloy is improved effectively and the wear resistance of the alloy is further reduced and the wear resistance of the alloy increases with the increase of Si content. In the homogenization annealing process, the Si phase in the hypereutectic Al-Si alloy of extrusion casting has gone through the process of melting, granulation and coarsening, and the distribution tends to be uniform and homogenized. The mechanical properties and wear resistance of the hypereutectic Al-Si alloy after the fire extrusion are improved. This is mainly due to the improvement of the phase appearance, size and distribution of the Si. When the 525oC homogenization annealing 8~12h, the Si phase particles are fine (the equivalent circle diameter is 2.0~2.5 mu m), the garden is whole, and the distribution is uniform, and the comprehensive mechanical and wear resistance of the alloy reaches the best. After hot extrusion, the microstructure of the hypereutectic Al-Si alloy ingot by squeezing casting was changed remarkably. The developed alpha -Al dendrites disappeared basically. The fine coralline eutectic Si phase was broken into small particles, and the average size was 2~4 mu m. The fine Si phase particles dispersed in the alloy matrix, and the fine particles of fine Si phase were distributed evenly in the soft distribution of the soft particles in the soft Si phase. The homogeneous structure of the Al matrix exerts the maximum potential of the alloy. The hot extrusion of the extruded casting Al-17.5Si two element alloy billet can greatly improve the properties of the alloy, especially the plasticity of the alloy. The thermal simulation experiment on the hypereutectic Al-Si alloy in squeezing casting was carried out, and the hypereutectic Al-S was found to be squeezed and cast. The stress level of I alloy under the same deformation condition is slightly higher than that of the gravity casting alloy. The thermal deformation activation energy of the alloy is 308.77kJ/mol. The reasonable hot processing parameters of the extruded cast alloy are: the deformation temperature 450oC~500oC, the strain rate 0.01s~ (-1) ~0.1s~ (-1). The tensile strength of the alloy is heated and the tensile strength is reached under this condition. The 332.1MPa increased by 135% compared with gravity casting, and the elongation was 13.51%, which increased 923.5%. compared with gravity casting.

【学位授予单位】：沈阳工业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG249.2

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