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亚共晶铝硅合金的变质处理及共晶硅的球化处理研究

作者:优质期刊论文发表网  来源:www.yzqkw.com  发布时间:2019/11/1 9:25:37  

摘要:铝硅合金不仅具有优良的铸造性能、抗疲劳性能和耐腐蚀性能,而且具有较高的比强度和综合力学性能,因而在航空、航天、军事及汽车工业领域得到了广泛应用。在亚共晶和共晶铝硅合金中,以针片状的形式存在共晶硅容易引起引应力集中,因此对铝硅合金的力学性能具有不利影响。

目前,已有的研究工作主要注重变质处理对共晶硅形态和尺寸及亚共晶铝硅合金力学性能的影响,未见有关变质处理对铝硅合金中初生α-Al的面积分数及合金力学性能影响的研究报道;此外,也少见有关采用热处理方法改变共晶硅形态的系统性研究报道。因此,开展变质处理对铝硅合金中初生α-Al面积分数及力学性能的影响、铝硅合金中共晶硅的球化退火研究,对拓宽亚共晶和共晶铝硅合金在工业领域中的应用具有一定的指导作用。

本文采用光学电子显微镜和扫描电子显微镜观察分析变质处理亚共晶铝硅合金的显微组织,采用万能电子试验机测试了合金的力学性能。研究了Al-3P单变质、Al-5Ti和Al-3P复合变质处理对亚共晶铝硅合金中初晶α-Al相和共晶组织相对数量及合金力学性能的影响;探索了退火温度和退火时间对共晶铝硅合金中共晶硅形态演变和合金力学性能的影响。研究取得的结果如下:

当变质温度为740℃时,随着Al-3P加入量的增加,Al-10Si合金中初生α-Al相面积分数的增加量呈现先增加后减少的变化趋势,当Al-3P加入量为0.6%时,初生α-Al相面积分数的增加量最大。在740℃下经0.6%Al-3P变质处理后,随着铝硅合金中硅含量增加,变质处理铝硅合金中初生α-Al相面积分数的增加量呈现逐渐增加的趋势。与未变质的Al-10Si合金相比,当变质温度为740℃、Al-3P加入量为0.6%时,变质处理Al-10Si合金的抗拉强度提高2.3%,伸长率提高47%。

在0.5%Al-5Ti变质Al-7Si合金的基础上,再用Al-3P对其进行复合变质处理后,Al-7Si合金中初生α-Al相面积分数增加;随着Al-3P加入量的增加,初生α-Al相面积分数不断减少。与0.5%Al-5Ti单变质的亚共晶铝硅合金相比,随着亚共晶铝硅合金中硅含量的增加,0.5%Al-5Ti和0.1%Al-3P复合变质亚共晶铝硅合金组织中初生α-Al相面积分数的增加量不断降低。与未变质的Al-7Si合金相比,0.5wt.%Al-5Ti+0.1wt.%Al-3P复合变质Al-7Si合金的抗拉强度和伸长率分别提高了19%和46%。与Al-5Ti变质Al-7Si合金相比,复合变质Al-7Si合金的抗拉强度和伸长率分别提高了10%和21%,其拉伸断口形貌呈现为明显的韧性断裂特征。

Al-12.6Si在500℃、560℃和577℃温度下退火时,针片状共晶硅可以转变成棒状或颗粒状。Al-12.6Si在500℃、560℃和577℃下的最佳退火时间分别为7、5和3小时,硅颗粒的表面形状因子分别为0.66、0.64和0.8;硅颗粒长度的平均值分别为仅为3.8μm、4.5μm和3.3μm。因此,从合金显微组织来看,Al-12.6Si在577℃进行球化退火时的效果最佳,500℃球化退火效果优于560℃。与铸态合金相比,当Al-12.6%Si合金在500和577℃分别退火7和3小时后,合金的拉伸强度分别下降9.8%和8.2%,但伸长率分别提高了66.7%和79.4%。因此,经过球化退火后合金的综合力学性能得到明显提高。

Al-Si alloy not only has excellent castingproperties and fatigue resistance as well as corrosion resistance, but also hashigh specific strength and comprehensive mechanical properties. So it is widelyused in aviation, aerospace, military and automotive industries. In themicrostructure of hypoeutectic and eutectic Al-Si alloys, the presence ofneedle-like eutectic silicon may cause stress concentration. Therefore, themechanical properties of Al-Si alloys are adversely affected.

At present, most studies mainly focus onthe effect of modification on the morphology and size of eutectic silicon andthe mechanical properties of hypoeutectic Al-Si alloys. There is no report onthe effect of modification treatment on the position of non-equilibriumeutectic points and the area fraction of primary α-Al in Al-Si alloys. Besides,there are few systematic studies on the effect of heat treatment on themorphology of eutectic silicon. Therefore, the influence of modification on thearea fraction of primary α-Al and the mechanical properties of Al-Si alloys aswell as the effect of annealing treatment on the spheroidization of eutecticsilicon in eutectic Al-Si alloy are necessary. The researches will play aguiding role in widening the application of hypoeutectic and eutectic Al-Sialloy in industrial.

The microstructure of modified hypoeutecticAl-Si alloy was observed and analyzed by optical microscope and scanningelectron microscope. The mechanical properties of the alloy were tested byuniversal electronic testing machine. The effects of Al-3P modification, Al-5Tiand Al-3P complex modification on the area fraction of primary α-Al andeutectic microstructure in hypoeutectic Al-Si alloy as well as the mechanicalproperties of the alloy were studied. The effects of annealing temperature andannealing time on the morphology evolution of eutectic slilicon in eutecticAl-Si alloy and the mechanical properties of the alloy were investigated. Theresults obtained from the study are as follows:

The increased area fraction of primary α-Alin Al-10Si alloy initially increased and then decreased when the amount ofadded Al-3P was increased at 740℃. The increased area fraction of primary α-Alreached the maximum when 0.6% Al-3P was added. The increased area fraction ofprimary α-Al in Al-Si alloy increased gradually as the Si content increasedwhen the alloy was modified at 740℃ with 0.6% Al-3P. Compared with theunmodified Al-10Si alloy, the tensile strength and elongation of the alloymodified at 740℃ with 0.6%Al-3P was increased by 2.3% and 47% resp ectively.

Compared with Al-7Si alloy modified with0.5%Al-5Ti, the area fraction of primary α-Al phase in Al-7Si alloy modifiedwith 0.5%Al-5Ti and Al-3P increased. With the increase of added amount ofAl-3P, the area fraction of primary α-Al phase decreased gradually. Compared withthe hypoeytectic Al-Si alloy, the increased amount of the area fraction ofprimary α-Al phase in the alloy modified with 0.5% Al-5Ti and 0.1% Al-3Pdecreased continuously with the increase of silicon content. Compared with theunmodified Al-7Si alloy, the tensile strength and elongation of Al-7Si alloymodified with 0.5wt.%Al-5Ti and 0.1wt.%Al-3P increased by 19% and 46%,respectively. Compared with Al-7Si alloy modified with Al-5Ti, the tensilestrength and elongation of Al-7Si alloy modified with 0.5wt.%Al-5Ti and0.1wt.%Al-3P increased by 10% and 21% respectively. The tensile fracture of thecomplex modified alloy showed obvious ductile fracture characteristics.

After Al-12.6Si was annealed at 500℃, 560℃,and 577℃, the flake eutectic silicon could be transformed into rod-like orgranular particles. The optimum annealing time for Al-12.6Si at 500℃, 560°C and577℃ was 7, 5 and 3 hours, respectively. The corresponding surface shapefactors of silicon particles are 0.66, 0.64 and 0.8, respectively. The correspondingaverage length of silicon particles is only 3.8 μm, 4.5μm and 3.3μm,respectively.

关键词:铝硅合金;变质处理;球化处理;微观组织;力学性能

Al-Si alloy; Modification; Spheroidization;Microstructure; Mechanical propertie

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