新型Al-Mg-Cu-Zn铝合金时效析出强化及成形性研究

发布时间：2018-02-06 00:18

  本文关键词： Al-Mg-Cu-Zn合金 合金成分 时效析出 中间形变热处理 成形性　出处：《北京科技大学》2017年博士论文　论文类型：学位论文

【摘要】：热处理不可强化的5xxx系Al-Mg合金因其优良的成形性和抗腐蚀性能而广泛运用于汽车行业。但由于强度较低而一般只用于汽车内板,并且在冲压成形后的烤漆过程中会出现烤漆软化。现有牌号5023合金(Al-5.2Mg-0.45Cu)因含有少量的Cu而具有烤漆强化作用,但其强度已经不能满足人们对汽车安全的性能要求。为了进一步提高合金强度,本论文在5023合金基础上添加Zn元素,并通过时效工艺的优化,充分发挥出所添加合金元素的析出强化作用,并对其作用机理进行了深入的分析。同时研究了新设计合金中Cu对时效析出强化和晶间腐蚀性能的影响规律和机理。最后探究了最终冷轧压下量和中间形变热处理工艺对新设计合金板材力学性能和成形性能的影响,得到以下结论:研究发现,添加Zn能促进GPB区和S相的析出,从而提高Al-5.2Mg-0.45Cu合金在180 下单级时效析出强化效果。Al-5.2Mg-0.45Cu-xZn(x=0.6、1.2、2.0)合金在峰时效状态下的组织是由细小针状的S-Al2MgCu相和粗大板条状的T-Mg32(AlZn)49相组成,其中S相含有少量的Zn,而T相含有少量的Cu。但随着Zn含量的增加,合金固溶态自然时效加剧,T4态板材在烤漆(180/30min)过程中会出现烤漆软化现象。针对Al-5.2Mg-0.45Cu-2.0Zn合金,80/12h的预时效处理能够形成稳定的GP区,不仅能够显著提高合金的时效析出强化效果,还能提高板材的室温稳定性,从而避免板材在烤漆过程中出现烤漆软化现象,合金T4P态烤漆后强度为271MPa,烤漆硬化增量为57MPa。合金预时效处理后的峰时效组织是由单一的细小弥散的T相组成,其平均成分为Al43 9Mg43 7Zn3.7Cu8.7,而GP区中Zn含量明显高于Cu。造成GP区和T相中Cu和Zn含量的巨大反差的原因是Cu在铝基体中的扩散速率远小于Zn。对于Al-5.2Mg-0.45Cu-1.2Zn合金,90℃/12h的预时效处理会降低合金的时效析出强化效果,其双级峰时效组织也是由S相和T相组成。在Al-5.2Mg-0.45Cu-2.0Zn合金中,Cu能促进GP区的形成,从而使双级峰时效形成的T相更加细小弥散,提高合金的时效析出强化效果。另外,Cu能使晶界无析出带宽度变窄,这不仅有利于提高合金强度,还能改善合金双级峰时效状态下的晶间腐蚀性能。从电化学角度来看,Cu能提高合金双级峰时效状态下的腐蚀电位和降低腐蚀电流,从而提高合金在该状态下的晶间腐蚀性能。针对Al-5.2Mg-0.45Cu-2.0Zn合金,最终冷轧压下量能在一定程度上细化晶粒,从而提高板材T4P态的成形性,但对板材力学性能几乎没有影响。另外,中间形变热处理工艺能明显细化晶粒,对T4P态板材的成形性具有明显的改善作用,杯突值由传统工艺的8.59mm提高至9.20mm,但对力学性能也几乎没有影响。作为成形性能的对比,退火态5182和T4态5023板材的杯突值分别为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，

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