【摘要】：ZL205A合金是由北京航空材料研究院于20世紀(jì)70年代研制成功的高強(qiáng)韌鑄造鋁合金,具有比強(qiáng)度高、耐腐蝕性和機(jī)械加工性能優(yōu)良等特點(diǎn),應(yīng)用于航空航天、兵器、冶金等領(lǐng)域,但結(jié)晶溫度區(qū)間較寬,在鑄造過程中易產(chǎn)生縮松、偏析等鑄造缺陷,并有晶間腐蝕和應(yīng)力腐蝕傾向,限制了在高性能機(jī)械零件和民用工業(yè)中的廣泛應(yīng)用。本文旨在拓寬高強(qiáng)度鑄造鋁合金在復(fù)雜薄壁鑄件和精密成形領(lǐng)域的產(chǎn)業(yè)化應(yīng)用,分別從鑄造工藝參數(shù)、微合金化和熱處理三個(gè)方面,研究了它們對ZL205A合金的微觀組織和性能的影響,并對作用機(jī)理做了詳盡和深入的分析,為進(jìn)一步控制材料的凝固行為和完善微觀組織精確調(diào)控理論奠定了基礎(chǔ)。澆注溫度和溫度梯度是控制材料凝固行為的關(guān)鍵工藝參數(shù)。通過改變澆注溫度(680℃~740℃),研究了不同壁厚(5 mm~25 mm)的鑄件在T6熱處理前后微觀組織和性能的變化。結(jié)果表明,隨著澆注溫度的升高,ZL205A鑄態(tài)合金中的θ相更傾向于以顆粒狀和細(xì)長條狀存在,且總體殘余量減少,分布也變得相對均勻規(guī)則,對基體的割裂減少。由壁厚引起的溫度梯度對θ相形貌和徑向成分梯度產(chǎn)生一定影響,殘余θ相中的Cu原子濃度隨壁厚增加而逐漸降低,降低溫度梯度能促進(jìn)Cu原子在基體中的固溶度,從而增強(qiáng)固溶強(qiáng)化效果。經(jīng)過T6熱處理后,晶體內(nèi)的殘余組織大幅度減少,合金元素在固溶處理和時(shí)效過程中基本上全都溶入基體,成分偏析降低,同時(shí)合金的組織致密度明顯高于鑄態(tài)。不同的微合金化元素與鋁合金的作用機(jī)理不同,形成的金屬間化合物與基體組織存在較大的差異,會對合金中二次相的析出過程產(chǎn)生重要影響,這將嚴(yán)重影響合金在固溶處理后的綜合力學(xué)性能。為此,本文比較并分析了在ZL205A合金中單獨(dú)添加微量Er和復(fù)合添加Er、Zr元素后θ相的偏析行為,并對材料鑄造性能、力學(xué)性能和斷裂性能的影響機(jī)理進(jìn)行研究。研究表明,單獨(dú)添加Er和復(fù)合添加Er、Zr元素均能顯著提高合金液的流動性,并減少縮松、縮孔、夾砂等鑄造缺陷的生成,有效地改善了ZL205A合金的鑄造性能。單獨(dú)添加Er元素會對Cu原子的擴(kuò)散和固溶過程產(chǎn)生較大影響,導(dǎo)致θ共晶相沿晶界發(fā)生偏聚,且隨著添加量的增加(0.1%~0.5%),晶體內(nèi)的殘余共晶組織增多。Er具有較高的化學(xué)活性,在凝固過程中容易吸附在原子團(tuán)和晶胚的界面上,降低θ,相的界面能和形核激活能,使TTT曲線左移,從而加速了固溶處理和時(shí)效過程中GP區(qū)和θ,相的脫溶進(jìn)度,并促使析出少量的θ平衡相。微量Er、Zr元素可以細(xì)化晶粒,使θ相分枝現(xiàn)象加重,且造成一定程度的偏析團(tuán)聚,最后導(dǎo)致晶界組織的寬度減小,甚至在有些地方熔斷為顆粒狀,而在交匯晶界處擴(kuò)展為片狀存在。T5處理能夠促使合金組織和成分均勻化,同時(shí)使溶質(zhì)原子充分?jǐn)U散,從而阻礙了變形過程中位錯(cuò)的運(yùn)動和亞晶界的遷移。
[Abstract]:ZL205A alloy is a kind of high strength and toughness cast aluminum alloy developed by Beijing Aeronautical Materials Research Institute in the 1970s. It has the characteristics of high specific strength, high corrosion resistance and excellent machining properties. It is used in aerospace, weapons, metallurgy and other fields. However, the wide range of crystallization temperature is easy to produce casting defects such as shrinkage, segregation and intergranular corrosion and stress corrosion, which limits its wide application in high performance mechanical parts and civil industry. The purpose of this paper is to expand the industrial application of high strength cast aluminum alloy in complex thin-walled castings and precision forming fields, respectively from three aspects: casting process parameters, microalloying and heat treatment. Their effects on microstructure and properties of ZL205A alloys were studied, and the mechanism of action was analyzed in detail, which laid a foundation for further controlling solidification behavior of materials and perfecting the theory of precise control of microstructure. Pouring temperature and temperature gradient are the key process parameters to control solidification behavior. The changes of microstructure and properties of castings with different wall thickness (5 mm~25 mm) before and after T6 heat treatment were studied by changing the pouring temperature (680 鈩，

本文編號：2211440