【摘要】：鎂合金輕量化的特點(diǎn)使其在結(jié)構(gòu)材料、功能材料和生物材料等方面具有巨大的應(yīng)用前景,被成為二十一世紀(jì)最有發(fā)展空間的"綠色工程材料",然而耐蝕性差卻使得其優(yōu)異的性能難以充分發(fā)揮出來。合金化和熱處理,可以有效提高鎂合金的高溫性能和耐蝕性能,是解決鎂合金應(yīng)用瓶頸的有效方法。試驗(yàn)材料為自制WE系列Mg-7Y-1Nd合金,選用熱處理方法,優(yōu)化工藝參數(shù),旨在提高M(jìn)g-7Y-1Nd合金的耐蝕性能。論文主要通過浸泡失重試驗(yàn)和極化曲線測試、電化學(xué)阻抗譜分析等電化學(xué)方法,并輔以合金表面形貌分析、成分分析、物相分析等手段,研究了固溶處理(T4)和固溶+時效處理(T6)對Mg-7Y-1Nd合金耐蝕性能的影響。試驗(yàn)結(jié)果表明鑄態(tài)Mg-7Y-1Nd合金中組織中有不規(guī)則骨骼狀相沿晶界分布,顆粒狀相在晶內(nèi)分布。固溶溫度535℃比515℃的第二相溶解得更徹底,當(dāng)固溶工藝參數(shù)為535℃×12h時,Mg-7Y-1Nd合金的固溶效果最好。當(dāng)固溶溫度為535℃時,隨著固溶時間的延長,晶界處不規(guī)則骨骼狀相逐漸溶入基體。鑄態(tài)和固溶態(tài)中第二相主要有Mg24Y5和Mg41Nd5,顆粒狀相主要為富Y化合物,骨骼狀相主要為富Nd化合物。時效態(tài)Mg-7Y-1Nd合金組織中析出相有Mg24Y5、Mg41Nd5和少量Mg12Nd,其形態(tài)有方形顆粒狀、棒狀、針狀及骨骼狀相。時效溫度越高,時效態(tài)Mg-7Y-1Nd合金中顆粒相越粗大,且較易出現(xiàn)聚集長大現(xiàn)象;時效時間的延長,使稀土的擴(kuò)散越充分,第二相顆粒分布越彌散,但時效時間過長會引起第二相聚集長大,對合金綜合性能造成不良影響。最終確定時效溫度225℃,時間14 h左右,T6態(tài)Mg-7Y-1Nd合金組織最為細(xì)致,第二相顆粒細(xì)小且彌散分布。研究發(fā)現(xiàn)固溶溫度為535℃的固溶處理可以有效改善鑄態(tài)Mg-7Y-1Nd合金在3.5%NaCl溶液中的耐蝕性能。隨著固溶時間的延長,Mg-7Y-1Nd合金的耐蝕性呈現(xiàn)先提高后降低的趨勢。固溶處理后Mg-7Y-1Nd合金的開路電位穩(wěn)定在-1.66V左右。時效溫度和時間T6態(tài)Mg-7Y-1Nd合金的耐蝕性均有影響。根據(jù)耐蝕性確定Mg-7Y-1Nd合金最佳熱處理工藝參數(shù)為:535℃×12h+225℃×14 h。鑄態(tài)Mg-7Y-1Nd合金的腐蝕失重速率、腐蝕電流密度和平衡電位分別為0.080 g·cm-2·d-1、1.0732×10-3 A·cm-2、-1.7526 V,采用最佳熱處理參數(shù)處理后Mg-7Y-1Nd合金的腐蝕失重速率、腐蝕電流密度和平衡電位分別為0.0122 g·cm-2·d-1、2.8018×10-4A·cm-2、-1.6382 V。通過電化學(xué)阻抗譜及腐蝕形貌分析,分別建立了 T4態(tài)和T6態(tài)Mg-7Y-1Nd合金腐蝕原理圖,固溶態(tài)合金的腐蝕類型主要為點(diǎn)蝕,時效態(tài)合金腐蝕的主要類型為點(diǎn)蝕和電偶腐蝕。固溶態(tài)Mg-7Y-1Nd合金的腐蝕產(chǎn)物由Mg(OH)2、MgO組成,而時效態(tài)合金腐蝕產(chǎn)物中出現(xiàn)了Mg41Nd5和Mg24Y5相。
[Abstract]:Due to its lightweight characteristics, magnesium alloys have great application prospects in structural materials, functional materials and biomaterials, and have become the most promising "green engineering materials" in the 21 century. However, the poor corrosion resistance makes it difficult to give full play to its excellent performance. Alloying and heat treatment can effectively improve the high temperature and corrosion resistance of magnesium alloy, and it is an effective method to solve the bottleneck of magnesium alloy application. The test material is WE series Mg-7Y-1Nd alloy. The corrosion resistance of Mg-7Y-1Nd alloy is improved by selecting heat treatment method and optimizing process parameters. In this paper, immersion weightlessness test, polarization curve test, electrochemical impedance spectroscopy and other electrochemical methods were used to analyze the surface morphology of the alloy, composition analysis, phase analysis and so on. The effects of solution treatment (T 4) and solution aging treatment (T 6) on the corrosion resistance of Mg-7Y-1Nd alloy were studied. The results show that there are irregular skeletal phases in the microstructure of as-cast Mg-7Y-1Nd alloys along the grain boundaries and granular phases in the grains. The solution temperature of 535 鈩，

本文編號：2327061