脉冲电流处理对Al-Si活塞合金凝固组织和性能的影响
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摘要
活塞作为发动机上的重要构件,担负着动力传输的重要任务。Al-Si合金以其较高的比强度及较好的尺寸稳定性,在活塞材料中已逐步占据了统治地位。其性能的每一次提高都必将伴随着机动车的一次“速度革命”。
脉冲电场细晶凝固技术始于国外,近些年在国内得到了快速发展。其所能作用的材料及其范围不断扩大,理论研究也不断深入,有望在不久的将来进行大规模工业应用。然而为了提高Al-Si合金的高温及耐磨性能,通常大量增加合金中Si的含量,因此使得合金凝固组织中的共晶Si、初生Si的形态和分布不合理,而且当加入变质剂时又易带来污染、过变质及合金成分不准确等一系列问题。
本文针对上述问题,制备了三种不同成分的Al-Si活塞合金试样,且对每种成分合金试样在不同过热度下进行了电脉冲处理(PECT)实验。并采用金相观察、SEM及EDS分析手段,对PECT前后及不同温度PECT下试样的凝固组织进行了分析,主要包括晶粒组织及第二相的形态、分布等。最后对合金试样的相关力学性能进行了测试。
结果表明:PECT能显著细化Al-Si活塞合金组织,使得含Si量小于12.6wt%合金晶粒尺寸减小;含Si量大于12.6wt%合金的一次枝晶臂间距(PDAS)的大小与PECT温度相关;合金凝固组织中初生Si、共晶Si及第二相的形态、分布特征在PECT前、后变化明显;结合对合金试样进行的强度、塑性及显微硬度的力学性能测试结果,得出了PECT对Al-Si活塞合金的最佳处理工艺。
运用热力学上关于正规溶液模型的假设,将Al-Si活塞合金熔体近似为Al-Si二元体系。根据Al-Si二元系固液两相的平衡条件,基于电脉冲孕育观点,分析了脉冲电场引起的熔体中组元相互作用能的变化对其发生固液相变时吉布斯自由能变化的影响。并结合脉冲电流提高形核率观点,解释了PECT后Al-Si活塞合金组织中初生Si、共晶Si在形貌、分布上变化的原因。
As an important part of the engines, pistons play a significant role in bearing and transporting the load. Among piston materials Al-Si alloys are becoming dominant gradually due to their better specific strength and shape stability. It is said that every time the properties of pistons are improved, the“speed up revolution”in engines will take place.
The pulse electric field grain refining technique that originates abroad takes much more progress domesticly. It is applied to many kinds of materials, and is investigated more deeply. It is expected to be used extensively in industrial fields. However, in order to improve pistons’wear resistance and high temperature resistance, we should increase the Si content in the Al-Si alloys. But this leads to uneven distributions in the morphology of the primary and eutectic Si phases. When we add chemical substance to modify them, it will also bring us problems of pollution, over-modification, and errors in composition controlling.
In light of the issue that implies above, three different compositions of Al-Si piston alloys were prepared, and were subjected to pulse electric current treatment (PECT) at different temperatures. In virtue of optical microscopy (OM), SEM and EDS, we observed and analyzed the solidification microstructures including the morphology of the matrix and the distribution and configuration of the secondary phases. Accordingly, the mechanical properties of the specimen prepared previously were tested.
The results indicate that PECT can refine the grains of Al-Si alloys, which refer to decreasing the grain size of the alloys with the Si content less than 12.6wt%. We also found the relations between the PECT temperature and the PDAS (primary dendrite arm spacing) of the alloys with Si content more than 12.6wt%. The morphology and distribution of the primary Si, eutectic Si, and the secondary phases varied obviously. Finally, we derived the best process parameter for PECT on Al-Si piston alloys from the testing of the tensile strength, elongation and microhardness of alloys prepared.
In order to elucidate the effect and mechanism of PECT, we thought the melt of Al-Si piston alloy as melt of Al-Si binary alloy approximately, in terms of the thermodynamic regular solution model. On the basis of equilibrium transformation of the solid-liquid phase of Al-Si binary alloy, we demonstrated that the PECT’s affect on the melt could arise from the variations of the interaction energy, which was based on an“electro-pulse modification”idea, and these variations resulted in the changes of Gibbs free energy in solid-liquid phase transformation. On the other hand, according to that PECT can accelerate the nucleation of Al, the growth of the primary Si and eutectic Si are surpressed, then changing their morphology and distributions.
脉冲电场细晶凝固技术始于国外,近些年在国内得到了快速发展。其所能作用的材料及其范围不断扩大,理论研究也不断深入,有望在不久的将来进行大规模工业应用。然而为了提高Al-Si合金的高温及耐磨性能,通常大量增加合金中Si的含量,因此使得合金凝固组织中的共晶Si、初生Si的形态和分布不合理,而且当加入变质剂时又易带来污染、过变质及合金成分不准确等一系列问题。
本文针对上述问题,制备了三种不同成分的Al-Si活塞合金试样,且对每种成分合金试样在不同过热度下进行了电脉冲处理(PECT)实验。并采用金相观察、SEM及EDS分析手段,对PECT前后及不同温度PECT下试样的凝固组织进行了分析,主要包括晶粒组织及第二相的形态、分布等。最后对合金试样的相关力学性能进行了测试。
结果表明:PECT能显著细化Al-Si活塞合金组织,使得含Si量小于12.6wt%合金晶粒尺寸减小;含Si量大于12.6wt%合金的一次枝晶臂间距(PDAS)的大小与PECT温度相关;合金凝固组织中初生Si、共晶Si及第二相的形态、分布特征在PECT前、后变化明显;结合对合金试样进行的强度、塑性及显微硬度的力学性能测试结果,得出了PECT对Al-Si活塞合金的最佳处理工艺。
运用热力学上关于正规溶液模型的假设,将Al-Si活塞合金熔体近似为Al-Si二元体系。根据Al-Si二元系固液两相的平衡条件,基于电脉冲孕育观点,分析了脉冲电场引起的熔体中组元相互作用能的变化对其发生固液相变时吉布斯自由能变化的影响。并结合脉冲电流提高形核率观点,解释了PECT后Al-Si活塞合金组织中初生Si、共晶Si在形貌、分布上变化的原因。
As an important part of the engines, pistons play a significant role in bearing and transporting the load. Among piston materials Al-Si alloys are becoming dominant gradually due to their better specific strength and shape stability. It is said that every time the properties of pistons are improved, the“speed up revolution”in engines will take place.
The pulse electric field grain refining technique that originates abroad takes much more progress domesticly. It is applied to many kinds of materials, and is investigated more deeply. It is expected to be used extensively in industrial fields. However, in order to improve pistons’wear resistance and high temperature resistance, we should increase the Si content in the Al-Si alloys. But this leads to uneven distributions in the morphology of the primary and eutectic Si phases. When we add chemical substance to modify them, it will also bring us problems of pollution, over-modification, and errors in composition controlling.
In light of the issue that implies above, three different compositions of Al-Si piston alloys were prepared, and were subjected to pulse electric current treatment (PECT) at different temperatures. In virtue of optical microscopy (OM), SEM and EDS, we observed and analyzed the solidification microstructures including the morphology of the matrix and the distribution and configuration of the secondary phases. Accordingly, the mechanical properties of the specimen prepared previously were tested.
The results indicate that PECT can refine the grains of Al-Si alloys, which refer to decreasing the grain size of the alloys with the Si content less than 12.6wt%. We also found the relations between the PECT temperature and the PDAS (primary dendrite arm spacing) of the alloys with Si content more than 12.6wt%. The morphology and distribution of the primary Si, eutectic Si, and the secondary phases varied obviously. Finally, we derived the best process parameter for PECT on Al-Si piston alloys from the testing of the tensile strength, elongation and microhardness of alloys prepared.
In order to elucidate the effect and mechanism of PECT, we thought the melt of Al-Si piston alloy as melt of Al-Si binary alloy approximately, in terms of the thermodynamic regular solution model. On the basis of equilibrium transformation of the solid-liquid phase of Al-Si binary alloy, we demonstrated that the PECT’s affect on the melt could arise from the variations of the interaction energy, which was based on an“electro-pulse modification”idea, and these variations resulted in the changes of Gibbs free energy in solid-liquid phase transformation. On the other hand, according to that PECT can accelerate the nucleation of Al, the growth of the primary Si and eutectic Si are surpressed, then changing their morphology and distributions.
引文
1傅恒志,柳百成,魏炳波.凝固科学技术与材料发展.国防工业出版社, 2005: P179
2 Hans Conrad. Influence of an electric or magnetic field on the liquid-solid transformation in materials and on the microstructure of the solid. Materials Science and Engineering .2000:205～212
3 Garnier Marcel. Electromagnetic processing of liquid materials in Europe. ISIJ International.1990,30(1):1～7
4 Li J M, Li S L, Li J et al. Modification of Solidification by Pulse Discharging. Scripta Metall,1994,31:1691～1694
5 Barnak J P, Sprecher A F, Conrad H. Colony (Grain) Size Reduction in Eutectic Pb-Sn Castings by Electropulsing. Scripta Metall Mater.1995,32(6):879～884
6范金辉,翟启杰.电流凝固技术的理论与实践.机械工程学报.2004,40(4):10～15
7陈文杰,廖希亮等.脉冲电流对Al-4.5Cu合金定向凝固组织的影响.特种铸造及有色合金.2006,26(8):523～525
8陈庆福,王建中等.电脉冲孕育细化CuAlNi合金的宏观组织与铸态形状记忆效应.材料科学与工艺,2001,9(3):240～242
9何树先,王俊等.高密度脉冲电流对A356铝合金低温熔体凝固组织的影响.金属学报. 2002,38(5):479～482
10 Masayuki NAKADA,Yuh SHIOHARA et al. Modification of Solidification Structures by Pulse Electric Discharging ISIJ International. 1990,30(1):27～33
11何树先,王俊等.高密度脉冲电流A356铝合金凝固组织的影响.中国有色金属学报.2002,12(3):426～429
12 M. Gao, G.. H. He, F. Yang, J. D. Guo, Z. X. Yuan, B. L. Zhou. Effect of electric current pulse on tensile strength and elongation of casting ZA27 alloy. Materials Science and Engineering A.2002,337:110~114
13陈宇,龚永勇等.高频脉冲电流对HT150灰铸铁凝固组织的影响.铸造.2004,53(8):611~613
14范金辉,李仁兴等.脉冲电流对过共晶灰口铸铁凝固组织的影响.钢铁研究学报.2004,16(5):59～62
15范金辉,华勤等.脉冲电流对奥氏体不锈钢凝固组织的影响.钢铁. 2003,38(5): 44～46
16刘达利,齐丕骧.新型铝活塞.国防工业出版社. 1999年:61~68
17李英龙,高彩茹等.铝硅合金的振动变质研究.轻合金加工技术. 1999, 27(11): 8～12
18王吉岱,闫承俊等.铝合金变质处理的现状和发展趋势.铸造.2005,54(9):844～846
19董光明,孙国雄等.共晶硅的变质.铸造.2005,54(1):1～5
20王玉琮,黄良余等.锶变质铝硅合金吸氢问题的研究及其精炼方法.铸造.1986 ( 8):32～36
21 K. Nogita , A.K. Dahle. Effects of boron on eutectic modification of hypoeutectic Al–Si alloys. Scripta Materialia. 2003,48:307~313
22 Fuoco R, Correa E R. Effect of modification treatment on micro-porosity formation in 356 A1 alloy,part 1:interdendritic feeding evaluation.AFS Transactions.1996,160:1151~1157
23 Kotte B.Strontium modification gives critical melt control. Modern Casting. 1985(5):690~695
24 Crosley P B. The modification of aluminum-silicon alloys.Modern Castings.1966, (3):89~100
25 Fom mei F. Modification treatments of A1-Si alloys.Aluminum.1977,146: 121~ 135
26 David P. Processing molten aluminum-part l: understanding silicon modification. Modern Casting.1990,1:24~ 27
27 Hurley T J, Atkinson R G. Effects of modification practice on aluminum A-356 alloys. AFS Transactions.1985, 39:291~296
28王建中.电脉冲孕育处理技术研究及液态金属团簇结构假说.北京科技大学博士学位论文. 1998年
29唐勇,王建中等.电脉冲对高碳钢凝固组织的影响.钢铁研究学报. 1999, 11(4): 44～47
30曹丽云,王建中等.电脉冲孕育(EPM)处理对ZL101合金凝固组织和力学性能的影响.铸造. 2001,50(10):590～593
31 Nakada M, Shiohara Y, Flemings M C. Modification of Solidification by Pulse Electric Discharging.ISIJ International.1990,30(1):27～33
32鄢红春,何冠虎等.脉冲电流对Sn-Pb合金凝固组织的影响.金属学报.1997, 33(4): 352～358
33范金辉,陈宇等.不同电压下脉冲电流对纯铝凝固组织的影响.特种铸造及有色合金,2004(6):27～29
34万刚,武保林等.脉冲电流对Zn- 42% Al合金定向凝固行为的影响方面的研究.铸造技术.2005,26(12):1124～1126
35甘长红,廖希亮等.脉冲电流对亚共晶Al-Si合金凝固组织的影响.铸造技术, 2006,27(3):252～254
36何树先,王俊等.高密度脉冲电流对过共晶Al- Si合金凝固组织的影响.中国有色金属学报.2002,12(2):275～278
37 Xiliang Liao, Qijie Zhai et al. Effects of electric current pulse on stability of solid/liquid interface of Al–4.5 wt% Cu alloy during directional solidification. Materials Science and Engineering A.2007:1~5
38 F. Li, L.L.Regel, et al. The influence of electric current pulses on the microstruc-ture of the MnBi/Bi eutectic. Journal of Crystal Growth. 2000,223:251～264
39顾根大.电场作用下金属定向凝固行为的研究.哈尔滨工业大学博士学位论文.1989年:23~71
40王建中.电脉冲孕育处理技术研究及液态金属团簇结构假说.北京科技大学博士学位论文.1998年
41訾炳涛,巴启先等.高密度脉冲电流作用下LY12铝合金的凝固组织.特种铸造及有色合金,2000,(4):4～6
42范金辉,翟启杰.物理场对金属凝固组织的影响.中国有色金属学报. 2002,12(S1):11～17
43 Dehong Lu,Yehua Jiang et al. Refinement of primary Si in hypereutectic Al–Si alloy by electromagnetic stirring. Materials Processing Technology. 2007, (189): 13~18
44 Xiliang Liao, Qijie Zhai et al. Refining mechanism of the electric current pulse on the solidification structure of pure aluminum. Acta Materialia.2007,(55):3103～3109
45 Wang J.N,Xie K. Grain size refinement of a TiAl alloy by rapid heat treatment Scripta Mater. 2000,43:441~446
46 J.W. Bae,T.W et at. Experimental investigation for rheology forming process of Al–7% Si aluminum alloy with electromagnetic system. Materials ProcessingTechnology.2007:1~5
47边秀房,王伟民等.金属熔体结构.上海交通大学出版社,2003年:P2、P3
48潘复生,张丁非等.铝合金及应用.化学工业出版社, 2006年: 173～179
49中国机械工程学会铸造专业学会铸造手册(铸造非铁合金).机械工业出版社,1993年:P79~P84
50胡汉起.金属凝固原理.第二版.机械工业出版社, 2000年: 190～194
51徐祖耀,李麟.材料热力学.第三版.科学出版社, 2005年: 99～101、88～91
52汪青杰,于智清等.脉冲电流对形核率影响机制的研究.辽宁工学院学报. 2006,26(4):227～229
2 Hans Conrad. Influence of an electric or magnetic field on the liquid-solid transformation in materials and on the microstructure of the solid. Materials Science and Engineering .2000:205～212
3 Garnier Marcel. Electromagnetic processing of liquid materials in Europe. ISIJ International.1990,30(1):1～7
4 Li J M, Li S L, Li J et al. Modification of Solidification by Pulse Discharging. Scripta Metall,1994,31:1691～1694
5 Barnak J P, Sprecher A F, Conrad H. Colony (Grain) Size Reduction in Eutectic Pb-Sn Castings by Electropulsing. Scripta Metall Mater.1995,32(6):879～884
6范金辉,翟启杰.电流凝固技术的理论与实践.机械工程学报.2004,40(4):10～15
7陈文杰,廖希亮等.脉冲电流对Al-4.5Cu合金定向凝固组织的影响.特种铸造及有色合金.2006,26(8):523～525
8陈庆福,王建中等.电脉冲孕育细化CuAlNi合金的宏观组织与铸态形状记忆效应.材料科学与工艺,2001,9(3):240～242
9何树先,王俊等.高密度脉冲电流对A356铝合金低温熔体凝固组织的影响.金属学报. 2002,38(5):479～482
10 Masayuki NAKADA,Yuh SHIOHARA et al. Modification of Solidification Structures by Pulse Electric Discharging ISIJ International. 1990,30(1):27～33
11何树先,王俊等.高密度脉冲电流A356铝合金凝固组织的影响.中国有色金属学报.2002,12(3):426～429
12 M. Gao, G.. H. He, F. Yang, J. D. Guo, Z. X. Yuan, B. L. Zhou. Effect of electric current pulse on tensile strength and elongation of casting ZA27 alloy. Materials Science and Engineering A.2002,337:110~114
13陈宇,龚永勇等.高频脉冲电流对HT150灰铸铁凝固组织的影响.铸造.2004,53(8):611~613
14范金辉,李仁兴等.脉冲电流对过共晶灰口铸铁凝固组织的影响.钢铁研究学报.2004,16(5):59～62
15范金辉,华勤等.脉冲电流对奥氏体不锈钢凝固组织的影响.钢铁. 2003,38(5): 44～46
16刘达利,齐丕骧.新型铝活塞.国防工业出版社. 1999年:61~68
17李英龙,高彩茹等.铝硅合金的振动变质研究.轻合金加工技术. 1999, 27(11): 8～12
18王吉岱,闫承俊等.铝合金变质处理的现状和发展趋势.铸造.2005,54(9):844～846
19董光明,孙国雄等.共晶硅的变质.铸造.2005,54(1):1～5
20王玉琮,黄良余等.锶变质铝硅合金吸氢问题的研究及其精炼方法.铸造.1986 ( 8):32～36
21 K. Nogita , A.K. Dahle. Effects of boron on eutectic modification of hypoeutectic Al–Si alloys. Scripta Materialia. 2003,48:307~313
22 Fuoco R, Correa E R. Effect of modification treatment on micro-porosity formation in 356 A1 alloy,part 1:interdendritic feeding evaluation.AFS Transactions.1996,160:1151~1157
23 Kotte B.Strontium modification gives critical melt control. Modern Casting. 1985(5):690~695
24 Crosley P B. The modification of aluminum-silicon alloys.Modern Castings.1966, (3):89~100
25 Fom mei F. Modification treatments of A1-Si alloys.Aluminum.1977,146: 121~ 135
26 David P. Processing molten aluminum-part l: understanding silicon modification. Modern Casting.1990,1:24~ 27
27 Hurley T J, Atkinson R G. Effects of modification practice on aluminum A-356 alloys. AFS Transactions.1985, 39:291~296
28王建中.电脉冲孕育处理技术研究及液态金属团簇结构假说.北京科技大学博士学位论文. 1998年
29唐勇,王建中等.电脉冲对高碳钢凝固组织的影响.钢铁研究学报. 1999, 11(4): 44～47
30曹丽云,王建中等.电脉冲孕育(EPM)处理对ZL101合金凝固组织和力学性能的影响.铸造. 2001,50(10):590～593
31 Nakada M, Shiohara Y, Flemings M C. Modification of Solidification by Pulse Electric Discharging.ISIJ International.1990,30(1):27～33
32鄢红春,何冠虎等.脉冲电流对Sn-Pb合金凝固组织的影响.金属学报.1997, 33(4): 352～358
33范金辉,陈宇等.不同电压下脉冲电流对纯铝凝固组织的影响.特种铸造及有色合金,2004(6):27～29
34万刚,武保林等.脉冲电流对Zn- 42% Al合金定向凝固行为的影响方面的研究.铸造技术.2005,26(12):1124～1126
35甘长红,廖希亮等.脉冲电流对亚共晶Al-Si合金凝固组织的影响.铸造技术, 2006,27(3):252～254
36何树先,王俊等.高密度脉冲电流对过共晶Al- Si合金凝固组织的影响.中国有色金属学报.2002,12(2):275～278
37 Xiliang Liao, Qijie Zhai et al. Effects of electric current pulse on stability of solid/liquid interface of Al–4.5 wt% Cu alloy during directional solidification. Materials Science and Engineering A.2007:1~5
38 F. Li, L.L.Regel, et al. The influence of electric current pulses on the microstruc-ture of the MnBi/Bi eutectic. Journal of Crystal Growth. 2000,223:251～264
39顾根大.电场作用下金属定向凝固行为的研究.哈尔滨工业大学博士学位论文.1989年:23~71
40王建中.电脉冲孕育处理技术研究及液态金属团簇结构假说.北京科技大学博士学位论文.1998年
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