【摘要】：鎂合金在高溫下容易燃燒,形成氧化夾雜降低產(chǎn)品性能,半固態(tài)成形工藝可在較低成形溫度下制備鎂合金產(chǎn)品,既能減少夾雜的產(chǎn)生又能延長(zhǎng)模具使用壽命。然而,目前用于半固態(tài)成形的鎂合金局限在AZ91等牌號(hào)合金上,這些合金熱處理強(qiáng)化作用較差,不利于發(fā)揮半固態(tài)壓鑄成形后可進(jìn)行熱處理的優(yōu)勢(shì),因此,研究適用于半固態(tài)成形的新型鎂合金勢(shì)在必行。Mg-Zn-Cu系列合金熱處理強(qiáng)化作用較好,但該合金系的半固態(tài)組織變化及優(yōu)化研究尚不深入。本文在ZC61合金的基礎(chǔ)上添加Ce元素,并借助XRD、OM、SEM、TEM等手段及拉伸試驗(yàn)來(lái)進(jìn)行以下研究。對(duì)ZC61+xCe合金組織和性能進(jìn)行研究后表明:ZC61合金的鑄態(tài)組織主要由基體α-Mg、CuMgZn及MgZn_2共晶相組成。Ce元素的添加量增加時(shí),有少量的Mg_12Ce相形成,合金晶粒逐步細(xì)化,抗拉強(qiáng)度和延伸率均呈先上升后下降的趨勢(shì)。合金斷裂方式由解理斷裂向準(zhǔn)解理斷裂轉(zhuǎn)變,再向解理斷裂轉(zhuǎn)變。在Ce含量為0.5%時(shí),合金晶粒最為細(xì)小,且抗拉強(qiáng)度和延伸率均達(dá)到最大值。采用等溫?zé)崽幚矸ㄑ芯緾e含量,保溫溫度和保溫時(shí)間對(duì)合金半固態(tài)組織的影響。結(jié)果表明:隨Ce含量增加,非枝晶顆粒明顯細(xì)化,且當(dāng)Ce含量達(dá)到0.7%時(shí),固相率會(huì)急劇下降。Mg-6Zn-1Cu-0.5Ce合金在600℃保溫25min時(shí),可獲得理想半固態(tài)組織,其顆粒尺寸、形狀因子和固相率分別為57μm、1.16和68%。另外,半固態(tài)組織中的固相主要由初生α_1(Mg)相和二次凝固的α_2(Mg)相組成。半固態(tài)組織演變過(guò)程為:共晶組織溶解與α-Mg的粗化→分離→球化→合并與長(zhǎng)大。顆粒分離機(jī)制包括亞晶界浸潤(rùn)機(jī)制和根部重熔機(jī)制。當(dāng)固、液兩相達(dá)到平衡階段時(shí),非枝晶顆粒發(fā)生Ostwald熟化。研究了熱處理對(duì)Mg-6Zn-1Cu-0.5Ce合金鑄態(tài)組織和性能的影響,結(jié)果表明:在405℃固溶24h后,共晶相會(huì)發(fā)生大量溶解,沿晶界分布的殘余共晶相以細(xì)小、彌散的顆粒狀存在。經(jīng)時(shí)效后,CuMgZn和MgZn_2等沉淀相分別在晶界和晶內(nèi)均有析出。提高時(shí)效溫度后,沉淀相的數(shù)量減少,抗拉強(qiáng)度和顯微硬度降低。在160℃時(shí)效20 h時(shí),抗拉強(qiáng)度和顯微硬度均達(dá)到最大值,分別為256MPa和84VHN。分析峰值時(shí)效下的TEM照片可知,垂直于滑移面的棒狀β_1'相強(qiáng)化作用明顯,而平行于盤(pán)狀滑移面的β_2'相的強(qiáng)化效果則弱了很多。對(duì)比斷口形貌可知:在鑄態(tài)拉伸時(shí),斷裂方式為沿晶及解理斷裂;在固溶態(tài)拉伸時(shí),斷裂方式為穿晶及準(zhǔn)解理斷裂;在時(shí)效態(tài)拉伸時(shí),斷裂方式為穿晶及混合斷裂。研究了熱處理對(duì)Mg-6Zn-1Cu-0.5Ce合金半固態(tài)組織的影響后表明,半固態(tài)組織的固溶轉(zhuǎn)變過(guò)程如下:共晶相溶解→α_2-Mg生長(zhǎng)并形成細(xì)小顆�！�(xì)小顆粒粗化及合并→初生顆粒合并→初生顆粒的粗化及長(zhǎng)大。半固態(tài)組織在時(shí)效后,沉淀相主要在二次凝固區(qū)析出。時(shí)效溫度提高后,析出相數(shù)量減少,且初生固相顆粒長(zhǎng)大。
[Abstract]:Magnesium alloy can easily burn at high temperature and form oxidized inclusions to reduce product properties. Semi-solid forming process can produce magnesium alloy products at lower forming temperature, which can not only reduce the inclusion generation but also prolong the service life of die. However, the magnesium alloys used in semi-solid forming at present are limited to AZ91 and other grade alloys, which have poor heat treatment strengthening effect, which is not conducive to the advantage of heat treatment after semi-solid die-casting forming. It is imperative to study the new magnesium alloy suitable for semi-solid forming. The heat treatment strengthening effect of Mg-Zn-Cu series alloy is good, but the research on the microstructure change and optimization of semi-solid alloy system is not deep. In this paper, Ce element is added to ZC61 alloy, and the following research is carried out by means of XRD,OM,SEM,TEM and tensile test. The microstructure and properties of ZC61 xCe alloy were studied. The as-cast structure of ZC61 alloy was mainly composed of matrix 偽-Mg,CuMgZn and MgZn_2 eutectic phase. When the addition of Ce element increased, a small amount of Mg_12Ce phase was formed, and the grain of ZC61 alloy was gradually refined. The tensile strength and elongation showed a trend of first rising and then decreasing. The fracture mode of alloy changed from cleavage fracture to quasi-cleavage fracture and then to cleavage fracture. When the content of Ce is 0.5, the grain size of the alloy is the smallest, and the tensile strength and elongation of the alloy reach the maximum value. The effects of Ce content, holding temperature and holding time on the semi-solid microstructure of the alloy were studied by isothermal heat treatment. The results show that with the increase of Ce content, the non-dendritic particles are refined obviously, and when the content of Ce reaches 0.7, the solid phase ratio will decrease sharply. The ideal semi-solid structure can be obtained by holding 25min at 600 鈩，

本文編號(hào)：2412075