本文關(guān)鍵詞： Al-Mg-Cu-Zn合金 合金成分 時效析出 中間形變熱處理 成形性　出處：《北京科技大學(xué)》2017年博士論文　論文類型：學(xué)位論文

【摘要】：熱處理不可強(qiáng)化的5xxx系A(chǔ)l-Mg合金因其優(yōu)良的成形性和抗腐蝕性能而廣泛運用于汽車行業(yè)。但由于強(qiáng)度較低而一般只用于汽車內(nèi)板,并且在沖壓成形后的烤漆過程中會出現(xiàn)烤漆軟化�，F(xiàn)有牌號5023合金(Al-5.2Mg-0.45Cu)因含有少量的Cu而具有烤漆強(qiáng)化作用,但其強(qiáng)度已經(jīng)不能滿足人們對汽車安全的性能要求。為了進(jìn)一步提高合金強(qiáng)度,本論文在5023合金基礎(chǔ)上添加Zn元素,并通過時效工藝的優(yōu)化,充分發(fā)揮出所添加合金元素的析出強(qiáng)化作用,并對其作用機(jī)理進(jìn)行了深入的分析。同時研究了新設(shè)計合金中Cu對時效析出強(qiáng)化和晶間腐蝕性能的影響規(guī)律和機(jī)理。最后探究了最終冷軋壓下量和中間形變熱處理工藝對新設(shè)計合金板材力學(xué)性能和成形性能的影響,得到以下結(jié)論:研究發(fā)現(xiàn),添加Zn能促進(jìn)GPB區(qū)和S相的析出,從而提高Al-5.2Mg-0.45Cu合金在180 下單級時效析出強(qiáng)化效果。Al-5.2Mg-0.45Cu-xZn(x=0.6、1.2、2.0)合金在峰時效狀態(tài)下的組織是由細(xì)小針狀的S-Al2MgCu相和粗大板條狀的T-Mg32(AlZn)49相組成,其中S相含有少量的Zn,而T相含有少量的Cu。但隨著Zn含量的增加,合金固溶態(tài)自然時效加劇,T4態(tài)板材在烤漆(180/30min)過程中會出現(xiàn)烤漆軟化現(xiàn)象。針對Al-5.2Mg-0.45Cu-2.0Zn合金,80/12h的預(yù)時效處理能夠形成穩(wěn)定的GP區(qū),不僅能夠顯著提高合金的時效析出強(qiáng)化效果,還能提高板材的室溫穩(wěn)定性,從而避免板材在烤漆過程中出現(xiàn)烤漆軟化現(xiàn)象,合金T4P態(tài)烤漆后強(qiáng)度為271MPa,烤漆硬化增量為57MPa。合金預(yù)時效處理后的峰時效組織是由單一的細(xì)小彌散的T相組成,其平均成分為Al43 9Mg43 7Zn3.7Cu8.7,而GP區(qū)中Zn含量明顯高于Cu。造成GP區(qū)和T相中Cu和Zn含量的巨大反差的原因是Cu在鋁基體中的擴(kuò)散速率遠(yuǎn)小于Zn。對于Al-5.2Mg-0.45Cu-1.2Zn合金,90℃/12h的預(yù)時效處理會降低合金的時效析出強(qiáng)化效果,其雙級峰時效組織也是由S相和T相組成。在Al-5.2Mg-0.45Cu-2.0Zn合金中,Cu能促進(jìn)GP區(qū)的形成,從而使雙級峰時效形成的T相更加細(xì)小彌散,提高合金的時效析出強(qiáng)化效果。另外,Cu能使晶界無析出帶寬度變窄,這不僅有利于提高合金強(qiáng)度,還能改善合金雙級峰時效狀態(tài)下的晶間腐蝕性能。從電化學(xué)角度來看,Cu能提高合金雙級峰時效狀態(tài)下的腐蝕電位和降低腐蝕電流,從而提高合金在該狀態(tài)下的晶間腐蝕性能。針對Al-5.2Mg-0.45Cu-2.0Zn合金,最終冷軋壓下量能在一定程度上細(xì)化晶粒,從而提高板材T4P態(tài)的成形性,但對板材力學(xué)性能幾乎沒有影響。另外,中間形變熱處理工藝能明顯細(xì)化晶粒,對T4P態(tài)板材的成形性具有明顯的改善作用,杯突值由傳統(tǒng)工藝的8.59mm提高至9.20mm,但對力學(xué)性能也幾乎沒有影響。作為成形性能的對比,退火態(tài)5182和T4態(tài)5023板材的杯突值分別為10.34mm和10.09mm。
[Abstract]:5xxx series Al-Mg alloy, which can not be strengthened by heat treatment, is widely used in automobile industry because of its excellent formability and corrosion resistance. During the process of stamping, the varnish will soften. The existing alloy 5023 Al-5.2Mg-0.45Cu) has the strengthening effect because of the small amount of Cu. But the strength of the alloy can not meet the requirements of automobile safety. In order to further improve the strength of the alloy, this paper adds Zn on the basis of 5023 alloy and optimizes the aging process. Fully exert the precipitation strengthening effect of the added alloy elements. At the same time, the effect of Cu on aging precipitation strengthening and intergranular corrosion was studied. Finally, the final cold rolling reduction and intermediate deformation heat were studied. The effect of the treatment process on the mechanical properties and formability of the newly designed alloy sheet. The following conclusions are obtained: the addition of Zn can promote the precipitation of GPB and S phases. Thus, the precipitation strengthening effect of Al-5.2Mg-0.45Cu alloy at the order order of 180 was improved. Al-5.2Mg-0.45Cu-xZnHX 0.6N 1.2. 2.0) the microstructure of the alloy under peak aging is composed of fine needle-like S-Al _ 2MgCu phase and coarse strip _ shaped T-Mg32 / Al _ (Zn) _ (49) phase, in which the S phase contains a small amount of Zn. However, with the increase of Zn content, the natural aging of the alloy in solid solution state is aggravated. During the process of 180 / 30 mins, the varnish softening will occur in the T4 state sheet. Aiming at the Al-5.2Mg-0.45Cu-2.0Zn alloy. 80 / 12 h pre-aging treatment can form stable GP region, which can not only significantly improve the aging precipitation strengthening effect of the alloy, but also improve the room temperature stability of the sheet metal. In order to avoid the softening phenomenon in the process of baking paint, the strength of alloy T4P after baking paint is 271MPa. The hardening increment of the varnish is 57 MPA. The peak aging microstructure of the alloy after preaging is composed of a single fine dispersed T phase. Its average composition is Al43 9mg 43 7Zn 3.7 Cu 8.7. However, the Zn content in GP region is significantly higher than that in Cu. The reason for the great contrast between Cu and Zn in GP region and T phase is that the diffusion rate of Cu in aluminum matrix is much lower than that in Zn. for Al-5.2Mg-. 0.45Cu-1.2Zn alloy. Pre-aging treatment at 90 鈩，

本文編號：1493123