發(fā)布時(shí)間：2018-01-28 18:09

  本文關(guān)鍵詞： AZ31鎂合金 交替擠壓 微觀組織 工藝優(yōu)化　出處：《哈爾濱理工大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：鎂合金具有低密度、高比強(qiáng)度及良好的再循環(huán)利用特性等系列優(yōu)點(diǎn),在輕量化、節(jié)能、環(huán)保等諸多方面受到青睞。室溫條件下,密排六方的晶體結(jié)構(gòu),導(dǎo)致鎂合金塑性較差,嚴(yán)重限制了鎂合金的應(yīng)用。擠壓可以令金屬處于三向壓應(yīng)力狀態(tài),能夠充分發(fā)揮它們的塑性,進(jìn)而獲得較細(xì)的晶粒組織結(jié)構(gòu)和很好的力學(xué)性能。因此,擠壓工藝特別適于鎂合金的制備和加工。節(jié)能減排、提高制品性能是擠壓工藝不斷改進(jìn)及創(chuàng)新過程中長期關(guān)注的研究熱點(diǎn)方向之一,為此,本文提出了一種新型擠壓方法-交替擠壓(AE)。交替擠壓工藝突破了傳統(tǒng)金屬擠壓工裝制造中沖頭為整體的設(shè)計(jì)理念,將其制成分體結(jié)構(gòu)形式,即用兩個(gè)或兩個(gè)以上的分體沖頭代替?zhèn)鹘y(tǒng)的整體結(jié)構(gòu)在擠壓過程中交替下行加載。盡管不同分體沖頭交替下行加載對(duì)生產(chǎn)效率有些影響,但卻收到了降低載荷和細(xì)化晶粒的實(shí)效。本文采用數(shù)值模擬與工藝實(shí)驗(yàn)相結(jié)合法,剖析了交替擠壓與常規(guī)擠壓在流動(dòng)行為、變形特征及載荷變化等方面的異同;利用金相顯微鏡(OM)、掃描電子顯微鏡(SEM)以及電子背散射技術(shù)(EBSD)等手段,深入研究了不同擠壓條件下晶粒尺寸的變化、斷口形貌等。結(jié)果表明:交替擠壓能顯著降低擠壓過程中的載荷值;并可改變擠壓過程中各部位金屬的流動(dòng)順序及模式,促使擠出流動(dòng)均勻性的提高;經(jīng)過交替擠壓工藝后,織構(gòu)的類型發(fā)生了改變,同時(shí)織構(gòu)具有減弱的趨勢(shì),有利于削弱材料的各向異性。在擠壓溫度350°C、總擠壓比為6和11的情況下,交替擠壓可以顯著細(xì)化晶粒,將原始坯料的平均晶粒尺寸,從385μm分別細(xì)化至6.5μm和5.3μm,并且晶粒細(xì)化能力隨著擠壓比的增加而增大;與此同時(shí),經(jīng)過交替擠壓后,原始坯料的斷裂方式發(fā)生改變,由脆性斷裂向韌性斷裂方向轉(zhuǎn)變。交替擠壓工藝還能使晶粒的位向發(fā)生改變,大角度晶界數(shù)量增加,有利于非基面滑移系的激活,有助于提高鎂合金的塑性。盡管交替擠壓中單道次內(nèi)實(shí)際的擠壓比減小了,但不同沖頭交替加載時(shí)在交界面處可產(chǎn)生附加剪切應(yīng)力,對(duì)微觀組織及綜合性能有重要影響。最后利用響應(yīng)面方法,優(yōu)化AZ31鎂合金交替擠壓成形工藝,并驗(yàn)證了模型的準(zhǔn)確性�？梢灶A(yù)知,隨著該工藝?yán)碚摰闹饾u成熟,有望為形/性一體化擠壓成形新方法研究提供新思路。
[Abstract]:Magnesium alloys have a series of advantages such as low density, high specific strength and good recycling characteristics. They are favored in many aspects, such as light weight, energy saving, environmental protection and so on. The plasticity of magnesium alloys is poor, which seriously limits the application of magnesium alloys. Extrusion can make metals in the state of three dimensional compressive stress, and can give full play to their plasticity. Therefore, the extrusion process is especially suitable for the preparation and processing of magnesium alloys, energy saving and emission reduction. Improving the properties of products is one of the hot research directions in the process of extrusion process improvement and innovation for a long time. In this paper, a new extrusion method, alternating extrusion (AEN), is proposed. The alternating extrusion process breaks through the traditional design concept of the punch as a whole in the manufacture of metal extrusion tools, and it is made into the form of split structure. That is to say, two or more split punch heads are used to replace the traditional integral structure in the process of extrusion alternately downlink loading, although different split punch alternately downlink loading has some effect on production efficiency. However, the effectiveness of reducing load and refining grain has been obtained. In this paper, the similarities and differences between alternate extrusion and conventional extrusion in flow behavior, deformation characteristics and load variation are analyzed by combining numerical simulation with technological experiments. The changes of grain size under different extrusion conditions were studied by means of optical microscope, scanning electron microscopy (SEM) and electron backscattering (EBSD). The results show that alternating extrusion can significantly reduce the load value in the extrusion process. The order and mode of metal flow in different parts of extrusion process can be changed, and the uniformity of extrusion flow can be improved. After the alternate extrusion process, the texture type has changed, and the texture has the tendency of weakening, which is favorable to weaken the anisotropy of the material, at the extrusion temperature of 350 擄C. When the total extrusion ratio is 6 and 11, the grain size can be significantly refined by alternating extrusion. The average grain size of the original billet is refined from 385 渭 m to 6.5 渭 m and 5.3 渭 m, respectively. The grain refinement ability increases with the increase of extrusion ratio. At the same time, after alternating extrusion, the fracture mode of the original billet changed from brittle fracture to ductile fracture. The increase in the number of large angle grain boundaries is conducive to the activation of non-basal slip systems and helps to improve the plasticity of magnesium alloys, although the actual extrusion ratio within a single pass decreases during alternating extrusion. However, additional shear stress can be produced at the interface between different punches under alternating loading, which has an important effect on the microstructure and comprehensive properties. Finally, the AZ31 magnesium alloy alternate extrusion process is optimized by using the response surface method. The veracity of the model is verified. It can be predicted that with the maturity of the process theory, it is expected to provide a new idea for the study of the new method of shape / sex integrated extrusion forming.
【學(xué)位授予單位】：哈爾濱理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG379

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本文編號(hào)：1471186