【摘要】：近年來(lái)為滿足汽車輕量化的要求,使用鎂合金、先進(jìn)高強(qiáng)度鋼(Advanced High Strength steel,AHSS)等輕型材料來(lái)制造汽車零部件越來(lái)越受到各大車企的重視。然而,鎂合金為密排六方的晶格結(jié)構(gòu),室溫塑性變形能力較差;先進(jìn)高強(qiáng)鋼較高的流變應(yīng)力,導(dǎo)致其成形力較大;同時(shí),鎂合金較低的彈性模量、先進(jìn)高強(qiáng)鋼較高的屈服強(qiáng)度,導(dǎo)致二者彎曲變形時(shí)回彈嚴(yán)重。這些問(wèn)題嚴(yán)重制約了這兩種輕型材料在汽車工業(yè)中的應(yīng)用。迫切需要針對(duì)這些輕型材料開(kāi)發(fā)新的沖壓工藝。電塑性成形技術(shù)是指材料變形時(shí)在其塑性變形區(qū)施加電流,以降低材料的變形抗力、提高材料塑性的成形技術(shù)。該技術(shù)已經(jīng)成功地應(yīng)用在拔絲、軋制等成形工藝上,并取得了良好的效果,同時(shí)電流對(duì)材料內(nèi)部的晶粒細(xì)化、損傷修復(fù)以及表面質(zhì)量的改善具有積極作用。因此,將電塑性成形工藝應(yīng)用于輕型材料的沖壓工藝中,有著很好的應(yīng)用前景。盡管電塑性成形技術(shù)已經(jīng)過(guò)多年的研究,然而相關(guān)的理論模型和實(shí)際應(yīng)用的研究尚不夠充分。理論模型方面,有學(xué)者根據(jù)材料的物理機(jī)理提出了一些流動(dòng)應(yīng)力的模型,但該類模型旨在描述電塑性效應(yīng)的物理意義,不便于工程應(yīng)用。另一方面,電塑性沖壓工藝的探索也剛剛起步,相關(guān)理論和技術(shù)都有待研究。針對(duì)以上問(wèn)題,本文開(kāi)展了以下工作:(1)通過(guò)AZ31B鎂合金和DP980 AHSS的電脈沖單向拉伸實(shí)驗(yàn)和等溫?zé)o電單向拉伸實(shí)驗(yàn),研究了脈沖電流對(duì)材料流變行為的影響,證實(shí)了電塑性效應(yīng)能降低AZ31B鎂合金的流動(dòng)應(yīng)力、改善其塑性,發(fā)現(xiàn)了DP980 AHSS的“反電塑性”效應(yīng);基于微觀組織分析,解釋了觀察到的現(xiàn)象,闡明了脈沖電流對(duì)材料微觀組織的影響。通過(guò)修改Johnson-Cook流動(dòng)應(yīng)力模型,建立了AZ31B鎂合金考慮脈沖電流影響的電塑性流動(dòng)應(yīng)力模型,并通過(guò)實(shí)驗(yàn)驗(yàn)證了模型的正確性。(2)通過(guò)AZ31B鎂合金和QP980 AHSS的電脈沖應(yīng)力松弛實(shí)驗(yàn)和等溫?zé)o電應(yīng)力松弛實(shí)驗(yàn)試驗(yàn),研究了脈沖電流對(duì)材料應(yīng)力松弛行為的影響,分析了溫度對(duì)QP980高強(qiáng)度鋼板應(yīng)力松弛行為的影響,指出了適合該材料電脈沖松弛的合適溫度;通過(guò)金相分析,解釋了脈沖電流對(duì)鎂合金應(yīng)力松弛的作用機(jī)理;基于蠕變力學(xué)基本理論,推導(dǎo)并建立了考慮脈沖影響的AZ31B鎂合金和QP980AHSS的應(yīng)力松弛模型,通過(guò)實(shí)驗(yàn)檢驗(yàn)了模型的正確性。(3)采用平面應(yīng)變假設(shè),基于考慮脈沖影響的AZ31B鎂合金和QP980AHSS的應(yīng)力松弛模型與Mises屈服準(zhǔn)則,將單軸應(yīng)力狀態(tài)下得到的應(yīng)力松弛模型擴(kuò)展到多軸應(yīng)力狀態(tài),建立了電脈沖輔助的V形彎曲回彈角的預(yù)測(cè)模型,并通過(guò)實(shí)驗(yàn)驗(yàn)證了模型的準(zhǔn)確性。通過(guò)微觀組織分析,對(duì)電脈沖抑制回彈的機(jī)理進(jìn)行了探討。(4)基于脈沖電流有利于降低流動(dòng)應(yīng)力、改善材料的塑性等優(yōu)點(diǎn),研發(fā)了若干脈沖電流輔助的典型塑性成形工藝,包括:電脈沖輔助的圓筒形件拉深工藝、滾輪包邊工藝和擴(kuò)孔工藝。工藝考慮了成形動(dòng)作的實(shí)現(xiàn)、脈沖電流的流通路徑和絕緣等設(shè)計(jì)要素,成功地將脈沖電流引入材料的塑性變形區(qū),明顯地改善了材料塑性變形能力。上述工藝為塑性相對(duì)較差或者難成形材料的塑性成形提供了新的思路,具有較好的應(yīng)用前景。
[Abstract]:In recent years, in order to meet the requirements of automobile lightweight, the use of magnesium alloys, advanced high strength steel (AHSS) and other light materials to manufacture automobile parts has attracted more and more attention of automobile enterprises. At the same time, the lower elastic modulus of magnesium alloy and the higher yield strength of advanced high strength steel lead to serious springback during bending deformation. These problems seriously restrict the application of these two light materials in automotive industry. The technique is a forming technique in which a current is applied to the plastic deformation zone of a material to reduce the deformation resistance and improve the plasticity of the material.The technique has been successfully applied to wire drawing, rolling and other forming processes and has achieved good results.At the same time, the current refines the grains in the material, repairs the damage and improves the surface quality. Therefore, the application of electroplastic forming technology in the stamping process of light materials has a very good application prospect. Although electroplastic forming technology has been studied for many years, the related theoretical model and practical application research are not enough. On the other hand, the exploration of electroplastic stamping process is just beginning, and the related theories and techniques need to be studied. In view of the above problems, the following work has been carried out in this paper: (1) through the AZ31B magnesium alloy and DP980 AHSS pulse. The effects of pulse current on the rheological behavior of AZ31B magnesium alloy were studied by uniaxial tensile test and isothermal uniaxial tensile test. It was proved that the electroplastic effect could reduce the flow stress and improve the plasticity of AZ31B magnesium alloy. By modifying Johnson-Cook flow stress model, the electroplastic flow stress model of AZ31B magnesium alloy considering the effect of pulse current was established, and the correctness of the model was verified by experiments. (2) The electro-pulse stress relaxation experiment and isothermal non-electric stress relaxation experiment of AZ31B magnesium alloy and QP980 AHSS were carried out. The effect of pulse current on stress relaxation behavior of QP980 high strength steel sheet was studied by experiment, and the effect of temperature on stress relaxation behavior of QP980 high strength steel sheet was analyzed. The stress relaxation model of AZ31B magnesium alloy and QP980AHSS considering the effect of pulse is deduced and established, and the correctness of the model is verified by experiments. (3) Based on the stress relaxation model and Mises yield criterion of AZ31B magnesium alloy and QP980AHSS considering the effect of pulse, the stress relaxation model under uniaxial stress state is obtained by using plane strain assumption. The model is extended to the multi-axial stress state, and the V-shaped bending springback angle prediction model assisted by electric pulse is established. The accuracy of the model is verified by experiments. The mechanism of restraining springback by electric pulse is discussed through microstructure analysis. (4) Based on the advantages of pulse current, such as reducing flow stress and improving plasticity of materials, the research and development are carried out. Several typical pulse current assisted plastic forming processes, including electric pulse assisted cylindrical drawing, roller edge wrapping and hole reaming, have been developed. The process considers the realization of forming action, the flow path of pulse current and insulation. The pulse current is successfully introduced into the plastic deformation zone of the material and is improved obviously. The above process provides a new idea for plastic forming of materials with relatively poor or difficult plasticity and has a good application prospect.
【學(xué)位授予單位】：上海交通大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TG386

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