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1、碩士學(xué)位論文摘要本文研究的目的是采用等溫?zé)崽幚韺Z91D鎂合金進(jìn)行非枝晶化,優(yōu)化成形工藝,得到性能良好的鎂合金成形件。在本實(shí)驗(yàn)中采用自行設(shè)計(jì)的壓鑄機(jī)壓室改變了傳統(tǒng)壓鑄機(jī)不能用于半固態(tài)壓鑄的狀況,加熱的壓室補(bǔ)充了合金液所散失的熱量,減緩了合金溶液在壓室中凝固的速度,保證金屬有較好的流動性,以滿足半固態(tài)鎂合金壓鑄成形的要求。實(shí)驗(yàn)中變換壓力和壓射速度,發(fā)現(xiàn)在其抗拉強(qiáng)度和伸長率都隨著壓力或速度的上升而增加。在保壓壓力35MPa,速度4.5m/s時(shí)其抗拉強(qiáng)度達(dá)到最大,為237.5MPa,伸長率為4.8%。在對半固態(tài)壓鑄零件進(jìn)行T4處理后,其力學(xué)性能均有所提高,其抗拉強(qiáng)度達(dá)到了248
2、MPa,伸長率達(dá)到了4.6%,硬度值達(dá)到了69HBS。分析成形件的沖頭位置、澆口位置、零件近端、零件遠(yuǎn)端組織,發(fā)現(xiàn)其晶粒度明顯小于等溫?zé)崽幚砗蟮模f明在充型過程中,沖頭的擠壓和內(nèi)澆口的剪切起到了細(xì)化晶粒的作用。在二次重熔坯料中的液相,經(jīng)過壓鑄成形之后明顯減少,從沖頭位置到零件遠(yuǎn)端液相率逐漸增加。通過對半固態(tài)成形試棒拉伸斷口形貌分析,發(fā)現(xiàn)半固態(tài)成形試棒的斷裂方式主要為沿晶斷裂。這是因?yàn)閴鸿T形成的組織為a·Mg和晶界處的共晶組織,p(Mgl7AIl2)為脆性相,這將導(dǎo)致在a—Mg和共晶組織的界面上產(chǎn)生脆性斷裂。關(guān)鍵詞:AZ9lD鎂合金;半固態(tài)壓鑄;熱處理;力學(xué)性能;組織演變;A
3、Z91D鎂合金半同態(tài)壓鑄T藝研究AbstractThetaskofthisstudyisforminggoodpartsbysemi—soliddiecastingviatooptimizingtheformingprocesses.Preparativeoftheno·dendriteAZ91Dmagnesiumalloybilletsbysemi·solidisothermalheattreatment.Thetraditionchambercannotbeusedinsemi—soliddiecasting,nOW,theconditionhaschanged,bec
4、ausethechamberwhichdesignedforsemi.soliddiecastingwasusedintheexperience.Theheatedchamberwhichcansupplythecaloriesfortheliquidalloyandabatethefreezingspeed.Theexcellentfluidityofthealloyfitthesemi—soliddiecastingofmagnesiumalloy.Theinfluencesoffillingspeedandpressureofdiecastingwasinvestig
5、ated.Theresultindicatedthatthetensilestrengthandelongationincreasedwithincreasingoffillingspeedorpressure.Thetensilestrengthhasthemaximalof237.5MPaandtheelongationis4.8%.AfterT4treatment.thetensilestrengthhasincreasedto248MPa,elongationis4.6%,andhardnesSiS69HBS.Thestructuresofdifferentposi
6、tionsofthecastingwereobserved.Comparingwiththeisothermalheattreatment,thegrainsizeissmallerafterdiecasting.Theresultshowsthattheplungerforgeplaysaroleongrainrefinement.Theliquidphaseinremeltbilletsisdecreaseaftershapedandthesolidphasehasincrasedfromthelocationpiercertothelocationfarawayfro
7、mingate.Thefracturemorphologyoftensiletestedspecimenshasanalysed.Theresultindicatedthatthefracturemorphologyofthesemi·soliddiecastingwasalonggrainboundariesmainly.ThestructureofdiecatingspecimensisprimaryU-MgandBphase.Thepphaseisfrangible,whichleadstofrangible