变频超声半连续铸造ZK60锭坯的组织与力学性能
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摘要
在半连续铸造255mm的ZK60镁合金锭坯过程中引入了可变频率的超声处理,并与传统的不施加超声处理和施加定频超声半连续铸造锭坯进行了对比,分析了不同处理方案下的ZK60镁合金的组织和力学性能,同时采用数值模拟获得了两种声场下声压随时间的变化规律。结果表明,较传统定频超声场,变频超声场能更大程度地细化晶粒,促进细小、球状的α-Mg的形成,同时可以改变第二相的形貌和分布。经由变频超声场处理后的ZK60镁合金,其心部抗拉强度为280MPa,伸长率为10.9%,相比未施加超声处理的铸锭分别增长了19.1%和78.7%,相比定频超声场处理的铸锭增长了11.6%、28.2%。铸锭不同部位出现的不同细化效果是由于超声衰减所致。变频超声场通过增强异质形核和枝晶破碎的效果来提高细化效果。
A varied ultrasonic technology was applied to refine the as-cast microstructure and improve the mechanical properties of a ZK60(Mg-Zn-Zr)alloy with255 mm in semi-continuous casting,which was analyzed comparatively with those of ones without ultrasonic treatment and static frequency ultrasonic semi-continuous casting.The change of acoustic pressure via time in two acoustic field was simulated by numerical method.The varied-frequency acoustic field can promote the formation of smallα-Mg globular grains and change the distribution and morphology ofβphases in the castings,greatly refining grain size in the alloy compared with that of static frequency field.Ultimate tensile strength and elongation of the alloy with varied-frequency field are increased to 280 MPa and 8.9%,respectively,which are 19.1%and78.7% higher than those of ones obtained from billet without ultrasonic treatment and are 11.6% and28.2% higher than that of ones by static-frequency ultrasound treated billets.Different refinement efficiencies appear in different regions of billet,which is attributed to the sound attenuation.The varied-frequency ultrasound can improve refinement effect by enhancing cavitation-enhanced heterogeneous nucleation and dendrite fragmentation effects.
A varied ultrasonic technology was applied to refine the as-cast microstructure and improve the mechanical properties of a ZK60(Mg-Zn-Zr)alloy with255 mm in semi-continuous casting,which was analyzed comparatively with those of ones without ultrasonic treatment and static frequency ultrasonic semi-continuous casting.The change of acoustic pressure via time in two acoustic field was simulated by numerical method.The varied-frequency acoustic field can promote the formation of smallα-Mg globular grains and change the distribution and morphology ofβphases in the castings,greatly refining grain size in the alloy compared with that of static frequency field.Ultimate tensile strength and elongation of the alloy with varied-frequency field are increased to 280 MPa and 8.9%,respectively,which are 19.1%and78.7% higher than those of ones obtained from billet without ultrasonic treatment and are 11.6% and28.2% higher than that of ones by static-frequency ultrasound treated billets.Different refinement efficiencies appear in different regions of billet,which is attributed to the sound attenuation.The varied-frequency ultrasound can improve refinement effect by enhancing cavitation-enhanced heterogeneous nucleation and dendrite fragmentation effects.
引文
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[3]周德钦,王贵福,王国军.镁合金的特点及其新技术发展[J].机械工程师,2006(1):25-27.
[4]STAIGER M P,PIETAK A M,HUADMAI J,et al.Magnesium and its alloys as orthopedic biomaterials:A review[J].Biomaterials,2006,27(9):1 728-1 734.
[5]JIN S L,LI Y W,LI Y B,et al.Modified directed melt nitridation of pure aluminum block using magnesium as an external dopant[J].Journal of Materials Science,2007,42(17):7 311-7 315.
[6]ZAKIYUDDIN A,YUN K,LEE K.Corrosion behavior of as-cast and hot rolled pure magnesium in simulated physiological media[J].Metals&Materials International,2014,20(6):1 163-1 168.
[7]ALI Y H,QIU D,JIANG B,et al.Current research progress in grain refinement of cast magnesium alloys:A review article[J].Journal of Alloys&Compounds,2015,619:639-651.
[8]ZHANG W Q,XIAO W L,WANG F,et al.Development of heat resistant Mg-Zn-Al-based magnesium alloys by addition of La and Ca:Microstructure and tensile properties[J].Journal of Alloys&Compounds,2016,684:8-14.
[9]LIU X,ZHANG Z Q,LE Q C,et al.The effects of ZnO particles on the grain refinement and mechanical properties of AZ31magnesium alloys[J].Transactions of the Indian Institute of Metals,2016,69(10):1-8.
[10]KIM Y H,KIM W J.Flame-resistant Ca-containing AZ31magnesium alloy sheets with good mechanical properties fabricated by a combination of strip casting and high-ratio differential speed rolling methods[J].Metals and Materials International,2015,21(2):374-381.
[11]邵志文,乐启炽,张志强,等.超声细化处理AZ80镁合金过程中的声场数值模拟[J].中国有色金属学报(英文版),2011,21(11):2 476-2 483.
[12]ESKIN G I.Principles of ultrasonic treatment:Application for light alloys melts[J].Advanced Performance Materials,1997,4(2):223-232.
[13]XI X,CEGLA F B,LOWE M,et al.Study on the bubble transport mechanism in an acoustic standing wave field[J].Ultrasonics,2011,51(8):1 014-1 025.
[14]RAE J,ASHOKKUMAR M,EULAERTS O,et al.Estimation of ultrasound induced cavitation bubble temperatures in aqueous solutions[J].Ultrasonics Sonochemistry,2005,12(5):325-329.
[15]VANHILLE C,CAMPOS-POZUELO C.Acoustic cavitation mechanism:A nonlinear model[J].Ultrasonics Sonochemistry,2012,19(2):217-220.
[16]FENG R,ZHAO Y Y,ZHU C P,et al.Enhancement of ultrasonic cavitation yield by multi-frequency sonication[J].Ultrasonics Sonochemistry,2002,9(5):231-236.
[17]LEE C D.Effect of grain size on the tensile properties of magnesium alloy[J].Materials Science&Engineering,2007,A459(1-2):355-360.
[18]LIU W C,DONG J,ZHANG P,et al.High cycle fatigue behavior of as-extruded ZK60 magnesium alloy[J].Journal of Materials Science,2009,44(11):2 916-2 924.
[19]LEE C D,SHIN K S.Effect of microporosity on the tensile properties of AZ91 magnesium alloy[J].Acta Materialia,2007,55(13):4 293-4 303.