本文選題：液態(tài)模鍛 + 7055鋁合金　； 參考：《北京交通大學(xué)》2016年碩士論文

【摘要】：7XXX系鋁合金中的7055鋁合金具有密度小、韌性好、比強(qiáng)度高、加工成本低和容易成型等優(yōu)良性能,已廣泛用于航空、航天、交通及其他方面的結(jié)構(gòu)件中。隨著科技的進(jìn)步和時代的快速發(fā)展,工業(yè)上對7055鋁合金材料的綜合性能提出了更高的要求。國內(nèi)外許多學(xué)者和專家對7055鋁合金的制備工藝、時效、均勻化、合金化等方面進(jìn)行了深入研究,進(jìn)展顯著。目前通過液態(tài)模鍛技術(shù)來制備7055合金及分析其組織和常規(guī)力學(xué)性能的研究,尚屬國內(nèi)空白。本文研究成果如下：(1)對液態(tài)模鍛7055鋁合金液鍛態(tài)和熱處理態(tài)試樣的各特征位置組織性能的研究表明：熱處理前同一液鍛件低壓時底部先凝固,所以底部晶粒最小,隨壓力增大頂部受壓使晶粒壓碎,致使試樣頂部晶粒尺寸比底部變小。熱處理后,各特征位置的微觀組織均得到改善,從而提高了力學(xué)性能,特別是心部元素固溶到基體較充分,力學(xué)性能提高顯著。(2)對不同壓力對液態(tài)模鍛7055鋁合金液鍛態(tài)和熱處理態(tài)試樣組織性能的研究表明：對于液鍛后試樣的同一位置隨壓力增大晶粒尺寸先減小再增大,然后呈減小趨勢。熱處理后的試樣顯微組織晶粒均增大,但析出的第二相起到了強(qiáng)化作用,固溶效果明顯,對于顯微組織晶粒尺寸,熱處理狀態(tài)下比液態(tài)模鍛狀態(tài)下均有所增大；隨著壓力的不斷提高,晶粒尺寸開始時減小然后逐漸增大；隨著壓力的進(jìn)一步增大,晶粒的尺寸呈現(xiàn)減小趨勢。(3)對液態(tài)模鍛7055鋁合金液鍛態(tài)試樣表面粗糙度的檢測分析研究表明：在上表面,由于低壓時壓頭過冷度大加快上表面凝固速度,表面粗糙度隨壓力增大而下降,隨著壓力增大,壓力使處于較高溫度的上表面發(fā)生鍛壓變形,使表面粗糙度降低。在下表面,表面粗糙度隨壓力增大而持續(xù)下降,然后趨于穩(wěn)定。在側(cè)面,表面粗糙度隨壓力增大而基本穩(wěn)定；在端面,表面粗糙度浮動較大。(4)對不同壓力對液態(tài)模鍛7055鋁合金液鍛態(tài)和熱處理態(tài)常規(guī)力學(xué)性能的影響規(guī)律研究表明：熱處理后的力學(xué)性能均比液鍛態(tài)的性能有明顯增加,其中硬度、拉伸強(qiáng)度、彎曲強(qiáng)度在各壓力條件下提高的幅度比例基本一致,而沖擊韌性波動較大,壓力75MPa時提升最大。熱處理前試樣拉伸強(qiáng)度、彎曲強(qiáng)度、硬度達(dá)最高時的壓力分別為125MPa、125MPa和75MPa,熱處理后試樣拉伸強(qiáng)度、彎曲強(qiáng)度、硬度最高時對應(yīng)的壓力分別為100MPa、125MPa和1OOMPa。熱處理后的材料斷裂韌性低壓時隨壓力增大而提高,在50MPa壓力以上時保持平穩(wěn)。
[Abstract]:7055 aluminum alloy in 7XXX series has been widely used in aviation, aerospace, transportation and other fields because of its low density, good toughness, high specific strength, low processing cost and easy forming. With the progress of science and technology and the rapid development of the times, the industrial requirements for the comprehensive properties of 7055 aluminum alloy materials are higher. Many scholars and experts at home and abroad have made great progress in the preparation, aging, homogenization and alloying of 7055 aluminum alloy. At present, the preparation of 7055 alloy by liquid die forging technology and the analysis of its microstructure and conventional mechanical properties are still blank in our country. The research results are as follows: (1) the microstructure and properties of liquid die forging 7055 aluminum alloy samples in liquid forging and heat treatment state are studied. The results show that the bottom of the same liquid forging is solidified at low pressure before heat treatment, so the grain at the bottom is the smallest. The grain size at the top of the sample is smaller than that at the bottom. After heat treatment, the microstructure of each characteristic position was improved, which improved the mechanical properties, especially the solid solution of the core elements to the matrix. The study on the microstructure and properties of liquid die forging 7055 aluminum alloy under different pressure shows that the grain size decreases first and then increases with the increase of pressure. Then it tends to decrease. After heat treatment, the microstructure grains of the samples increased, but the second phase of precipitation played a strengthening role, and the effect of solid solution was obvious. The grain size of the microstructure in the heat treatment state was larger than that in the liquid die forging state. With the increasing of the pressure, the grain size decreases at first and then increases gradually, and with the further increase of the pressure, The analysis of the surface roughness of liquid die forging 7055 aluminum alloy shows that, on the upper surface, the solidification rate of the upper surface is accelerated because of the high undercooling of the pressure head at low pressure. The surface roughness decreases with the increase of pressure, and with the increase of pressure, the upper surface at higher temperature is deformed by forging, and the surface roughness decreases. On the lower surface, the surface roughness decreases continuously with the increase of pressure, and then tends to stabilize. On the side, the surface roughness is basically stable with the increase of pressure; on the end surface, The effect of different pressure on the conventional mechanical properties of liquid and heat treated 7055 aluminum alloy was studied. The results showed that the mechanical properties of 7055 aluminum alloy after heat treatment were obviously higher than those of liquid forging, and the hardness of them was higher than that of liquid forging. The tensile strength and flexural strength are basically the same under various pressure conditions, while the impact toughness fluctuates greatly, and the maximum increase is under pressure 75MPa. Before heat treatment, the tensile strength, bending strength and hardness were 125 MPA and 75 MPA, respectively. After heat treatment, the tensile strength, bending strength and the corresponding pressure at the highest hardness were 100 MPA and 1 OOMPA, respectively. After heat treatment, the fracture toughness of the material increases with the increase of pressure at low pressure, and remains stable above the 50MPa pressure.
【學(xué)位授予單位】：北京交通大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2016
【分類號】：TG319

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