【摘要】：近年來,隨著我國汽車工業(yè)的飛速發(fā)展,鋁合金作為目前交通工具輕量化中替代鋼鐵的首選材料,逐漸在汽車行業(yè)中得到越來越廣泛地運用。在汽車用鋁合金中,真空壓鑄鋁合金以其良好的表面質(zhì)量、優(yōu)異的力學(xué)性能以及較高的材料利用率等優(yōu)點,在汽車用鋁合金零部件中占有極其重要的地位。以Aural-2(Al-10Si-0.3Mg)為代表的高塑性壓鑄鋁合金的開發(fā)推動了鋁合金大鑄件在汽車結(jié)構(gòu)件上的應(yīng)用。本文以厚度為2.5mm和5.0mm的真空壓鑄Aural-2(Al-10Si-0.3Mg)鋁合金薄板作為研究對象。在汽車工業(yè)上,真空壓鑄Al-10Si-0.3Mg合金通常用于制造形狀復(fù)雜的大型薄壁汽車部件。汽車的復(fù)雜結(jié)構(gòu)將使不同部位對合金構(gòu)件的厚度要求存在差異,使得合金在制作成壓鑄部件后存在尺寸不均的問題,因此本文首先將對不同壁厚合金的鑄態(tài)組織進行對比分析,研究冷卻速率對合金凝固組織和性能的影響。此外,為了改善合金的綜合力學(xué)性能,特別是塑性方面,本文隨后將對合金進行固溶和時效處理,采用光學(xué)顯微鏡(OM)、掃描電子顯微鏡(SEM)和透射電子顯微鏡(TEM)等分析手段,并通過室溫力學(xué)性能拉伸試驗,系統(tǒng)研究熱處理工藝對合金的微觀組織和力學(xué)性能的影響,獲得合金的最佳熱處理工藝參數(shù)。同時通過觀察熱處理后合金的拉伸斷口形貌和拉伸斷口縱向面的微觀組織,對影響合金拉伸斷裂的因素和合金的斷裂行為進行分析探討。研究結(jié)果表明:(1)兩種壁厚合金的鑄態(tài)組織沿厚度方向均呈不均勻分布:2.5mm厚合金的鑄態(tài)組織沿厚度方向呈梯度分布,可以觀察到不太明顯的 三明治‖結(jié)構(gòu),而5mm厚合金的鑄態(tài)組織沿厚度方向呈明顯的 三明治‖結(jié)構(gòu)分布,即表層區(qū)+心部區(qū)+表層區(qū)。隨著冷卻速率的增加,合金的微觀組織得到細(xì)化。相較于5.0mm厚合金,2.5mm厚合金表層細(xì)晶區(qū)比例由35%增加到40%左右,同時合金中共晶硅的纖維化趨勢增加。鑄態(tài)下,2.5mm厚合金的硬度、抗拉強度、屈服強度及伸長率依次為106.9HV、303.1MPa、164.2MPa、7.6%。;當(dāng)冷卻速率較低,合金厚度為5.0mm時,其硬度、抗拉強度、屈服強度及伸長率分別下降到91HV、227.4MPa、115.3MPa、5.8%。(2)固溶處理將提高合金基體內(nèi)固溶的Mg元素和Si元素含量。同時在此過程中,合金中的共晶硅形貌將向粒狀化和球狀化轉(zhuǎn)變。在時效處理過程中,2.5mm厚合金將有沉淀硬化相析出,主要是占主導(dǎo)的細(xì)針狀β‖相、少量桿狀β’相和顆粒Si相。其中,β‖析出相的橫斷面直徑約10-18nm,長度約200-800nm;β’析出相的橫斷面直徑約20-38nm,長度為600-1400nm,兩者均沿著基體的001方向分布。(3)人工時效可以顯著改善合金的力學(xué)性能。在本文設(shè)定的熱處理工藝條件下,2.5mm厚合金在最佳熱處理工藝參數(shù)450℃/1.5h+225℃/1h下,其抗拉強度、屈服強度及伸長率依次為212.2MPa、113.1MPa、16%;5.0mm厚合金在最佳熱處理工藝參數(shù)450℃/1.5h+225℃/2h下,其抗拉強度、屈服強度及伸長率依次為184.5MPa、118.7MPa、8.73%。(4)通過對合金的拉伸斷口形貌和拉伸斷口縱向面微觀組織的分析可知,熱處理后合金的斷裂類型為韌性斷裂,同時合金中共晶硅顆粒的尺寸和取向?qū)辖鸬睦煨阅墚a(chǎn)生影響。合金在拉伸過程中,將發(fā)生第二相的開裂、微裂紋的萌生與生長和微裂紋的連接三個過程,最終合金的斷裂方式將是沿晶斷裂和穿晶斷裂兩種方式的結(jié)合。
[Abstract]:In recent years, with the rapid development of the automobile industry in China, the aluminum alloy has been widely used in the automobile industry as the preferred material for replacing iron and steel in the light weight of the current vehicle. In the aluminum alloy for automobiles, the vacuum die-casting aluminum alloy has the advantages of good surface quality, excellent mechanical property and high material utilization ratio, and plays an extremely important role in automobile aluminum alloy parts. The development of high-plastic die-cast aluminum alloy represented by Auural-2 (Al-10Si-0. 3Mg) has promoted the application of the aluminum alloy large-cast to the structural parts of the automobile. The Al-10Si-0.3Mg (Al-10Si-0. 3Mg) aluminum alloy sheet with a thickness of 2. 5 mm and 5. 0mm is used as the research object. In the automotive industry, the vacuum die-cast Al-10Si-0. 3Mg alloy is commonly used to make large thin-walled automobile parts with complex shapes. The complicated structure of the automobile will make the difference of the thickness of the alloy component in different parts, so that the alloy has the problem of non-uniform size after making the die-casting part, The effect of cooling rate on the microstructure and properties of the alloy was studied. In addition, in order to improve the comprehensive mechanical properties of the alloy, in particular the plastic aspect, the alloy is subjected to solid solution and aging treatment, and an optical microscope (OM), a scanning electron microscope (SEM) and a transmission electron microscope (TEM) are used to analyze the alloy. The effect of heat treatment on the microstructure and mechanical properties of the alloy was studied by mechanical tensile test at room temperature, and the optimum heat treatment process parameters of the alloy were obtained. At the same time, by observing the tensile fracture morphology of the alloy after heat treatment and the microstructure of the longitudinal surface of the tensile fracture, the factors affecting the tensile fracture of the alloy and the fracture behavior of the alloy are analyzed. 鐮旂┒緇撴灉琛ㄦ槑:(1)涓ょ澹佸帤鍚堥噾鐨勯摳鎬佺粍緇囨部鍘氬害鏂瑰悜鍧囧憟涓嶅潎鍖，

本文編號：2348877