AZ91D镁合金压铸样品仿真分析及腐蚀行为研究
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摘要
通过铸造仿真软件(MAGMA)对AZ91D镁合金笔记本电脑底外壳压铸过程进行仿真分析,采用压铸方法及表面化学转化后处理制备样品。利用扫描电镜及能谱仪分析了样品的表面及亚表面的结构特征,极化曲线和盐雾实验用来研究样品的腐蚀行为。仿真分析结果表明,样品的填充时间为0.012 1 s.实验结果表明,在浇口位置附近基体微孔含量较低,而在填充远端,即排气孔位置,微孔含量明显增多。通过对样品内部气体含量的仿真分析进一步验证了这一结果。微孔主要是由熔融镁合金的高温使模具表面喷涂的脱模剂水分呈爆炸式膨胀导致的。另外,相对浇口位置样品而言,填充远端样品的耐腐蚀性严重降低,这是由于远端样品的化学转化膜不连续和不完整导致的,而这恰恰与微孔有直接的关系。
The die-casting process of a notebook computer bottom shell was simulated using MAGMA software.The AZ91D shell with a complex geometry was manufactured with die-cast process.Chemical conversion was applied to provide surface protection against physical and chemical damage.The surface layer characteristics of the component were investigated using scanning electron microscopy coupled with energy-dispersive spectrometer.Corrosion behaviour was also studied by polarisation curves and salt spray test.The results of simulation showed that the filling process was completed in 0.012 1 s.The experiment results showed that the microporosity was higher at the end of the filling process than the regions that filled first.This result was further confirmed by simulation of air content in the component using MAGMA software.The main formation mechanism of microporosity was explosive expansion of dilution water containing the lubricant when the molten Mg alloy entered the die cavity.Additionally,the corrosion resistance of the sample at the end of the filling was severely poorer than the regions that filled first,which was caused by discontinuous conversion coatings.The discontinuous coatings just resulted from surface microporosity.
The die-casting process of a notebook computer bottom shell was simulated using MAGMA software.The AZ91D shell with a complex geometry was manufactured with die-cast process.Chemical conversion was applied to provide surface protection against physical and chemical damage.The surface layer characteristics of the component were investigated using scanning electron microscopy coupled with energy-dispersive spectrometer.Corrosion behaviour was also studied by polarisation curves and salt spray test.The results of simulation showed that the filling process was completed in 0.012 1 s.The experiment results showed that the microporosity was higher at the end of the filling process than the regions that filled first.This result was further confirmed by simulation of air content in the component using MAGMA software.The main formation mechanism of microporosity was explosive expansion of dilution water containing the lubricant when the molten Mg alloy entered the die cavity.Additionally,the corrosion resistance of the sample at the end of the filling was severely poorer than the regions that filled first,which was caused by discontinuous conversion coatings.The discontinuous coatings just resulted from surface microporosity.
引文
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[2]Upton B,Allsop D-F,Kennedy D,et al.压力铸造[M].北京:机械工业出版社,1988,150-152.
[3]王罡,袁娘,熊守美,等.压室慢压射过程流场模拟[J].铸造,2004,53(11):909-912.
[4]Dabayeh A-A,Berube A-J,Topper T-H.An experimental study of the effect of a flaw at a notch root on the fatigue life of cast Al[J].Int.J.Fatigue,1998,20(7):517-530.
[5]Caceres C-H,Selling B-I.Casting defects and tensile properties of an Al-Si-Mg alloy[J].Mater.Sci.Eng.A,1996,220:109-116.
[6]Liu B-S,Wei Y-H,Hou L-F.Formation Mechanism of Discoloration on Die-Cast AZ91D Components Surface After Chemical Conversion[J].J.Mater.Eng.Perform.,2013,22:50-56.
[7]Liu B-S,Wei Y-H,Hou L-F,et al.Blistering failure analysis of organic coatings on AZ91D Mg-alloy components[J].Eng.Fail.Anal.,2014,42:231-239.
[8]Cui X-F,Jin G,Yang Y-Y,et al.Study of gadolinium based protective coating for magnesium alloys[J].Surf.Eng.,2012,28(10),719-724.
[9]Yan H,Zhuang W-W,Hu Y,et al.Numerical simulation of AZ91Dalloy automobile plug in pressure die casting process[J].J.Mater.Process.Technol.,2007,187-188:349-353.
[10]Stefanescu D-M.Casting[M].‘ASM Metals Handbook’,9th edn,Vol.15,Die-Casting,(ed.Lionel J.D.Sully),611-632;1988,Materials Information Company,ASM International.
[11]Teng X,Mae H,Bai Y,et al.Pore size and fracture ductility of aluminum low pressure die casting[J].Eng.Fract.Mech.,2009,76:983-996.
[12]Wang L-H,Turnley P,Savage G.Gas content in high pressure die-castings[J].J.Mater.Process.Technol.,2011,211(9):1510-1515.
[13]刘宝胜.AZ91D镁合金压铸工艺对表面处理的影响及表面喷涂金属涂层研究[D].太原:太原理工大学,2014.
[14]Aghion E,Moscovitch N,Arnon A.The correlation between wall thickness and properties of HPDC magnesium alloys[J].Mater.Sci.Eng.A,2007,447(1-2):341-346.
[15]JIS Z 2371,Methods of Salt Spray Apparatus[Z].2010.
[16]Wei Y-H,Yin G-S,Hou L-F,et al.Ichinose H.Formation mechanism of pits on the surface of thin-wall die-casting magnesium alloy components[J].Eng.Fail.Anal.,2006,13:558-564.
[17]Lee S-G,Gokhale A-M,Patel G-R,Evans M.Effect of process parameters on porosity distributions in high-pressure die-cast AM50 Mg-alloy[J].Mater.Sci.Eng.A,2006,427(1-2):99-111.