【摘要】：不銹鋼與鋁合金在擴(kuò)散連接過程中,由于物理、化學(xué)性能差異較大而使兩者的有效連接很難實(shí)現(xiàn),同時(shí)連接過程中生成的Fe-Al金屬間化合物嚴(yán)重惡化接頭的力學(xué)性能。因此,本論文采用在擴(kuò)散連接前對(duì)不銹鋼和鋁合金進(jìn)行表面自納米化處理的方式,通過細(xì)化材料表面晶粒來達(dá)到改善接頭綜合性能的目的。本論文分別對(duì)304不銹鋼和7A04鋁合金進(jìn)行表面機(jī)械研磨(Surface mechanical attrition technology, SMAT)和超音速微粒轟擊(Supersonic fine particles bombarding,SFPB)處理,采用多種試驗(yàn)方法對(duì)表面層組織進(jìn)行表征分析,研究結(jié)果表明分別在不銹鋼和鋁合金表面制備出一定厚度的納米晶組織。為了確定所制備納米品組織的熱穩(wěn)定性溫度,以制定表面自納米化304不銹鋼與7A04鋁合金擴(kuò)散連接工藝,分別對(duì)表面自納米化304不銹鋼和7A04鋁合金的納米組織進(jìn)行不同溫度的等溫退火,并采用金相顯微鏡、X-射線衍射(XRD)、顯微硬度儀研究?jī)煞N金屬表層納米晶組織。最后通過掃描電鏡、顯微硬度、剪切強(qiáng)度和X-射線衍射分析接頭的組織和性能。研究結(jié)果表明,經(jīng)過表面自納米化處理后,在304不銹鋼和固溶時(shí)效態(tài)7A04鋁合金表面分別制備出了厚度為100μm和20μm的納米晶組織,不銹鋼的晶粒細(xì)化機(jī)制為機(jī)械孿晶、位錯(cuò)運(yùn)動(dòng)和應(yīng)變誘發(fā)馬氏體相變的共同作用,而鋁合金的細(xì)化機(jī)制則是位錯(cuò)運(yùn)動(dòng)的結(jié)果。表面自納米化處理在細(xì)化晶粒的同時(shí)還使材料中的晶界數(shù)量和缺陷密度劇烈增加,這將有利于改善擴(kuò)散連接接頭性能。對(duì)兩種金屬表面納米晶組織熱穩(wěn)定性分析研究表明,304不銹鋼納米晶組織在不高于600℃時(shí)具有良好的熱穩(wěn)定性,而7A04鋁合金納米晶組織在不高于500℃時(shí)具有一定熱穩(wěn)定性。將表面自納米化不銹鋼和鋁合金分別在400℃、425℃、450℃、475℃和500℃的溫度下保溫0.5h-4h,連接壓力設(shè)定為6MPa,真空度在1Pa左右,進(jìn)行真空擴(kuò)散連接試驗(yàn),對(duì)連接后的試樣進(jìn)行剪切強(qiáng)度的測(cè)試,450℃溫度連接2h后的剪切強(qiáng)度達(dá)到55MPa,剪切強(qiáng)度隨著溫度的上升和連接時(shí)間的延長(zhǎng)而先上升再下降。分析不同工藝下接頭處的物相組成,生成的金屬間化合物為FeAl、AlFe3、Al3Fe和Fe2Al5。綜合研究結(jié)果,表面自納米化處理能夠有效的提高不銹鋼和鋁合金在擴(kuò)散連接過程中原子的擴(kuò)散系數(shù),降低原子擴(kuò)散激活能,能夠在較低的溫度下實(shí)現(xiàn)兩種材料的有效連接,改善連接接頭力學(xué)性能。
[Abstract]:In the diffusion bonding process of stainless steel and aluminum alloy, the physical and chemical properties are quite different, which makes the effective bonding between stainless steel and aluminum alloy difficult to be realized. Meanwhile, the mechanical properties of the joints are seriously deteriorated by the Fe-Al intermetallic compounds generated during the bonding process. Therefore, in this paper, the surface self-nanocrystalline treatment of stainless steel and aluminum alloy was carried out before diffusion bonding, and the comprehensive properties of the joints were improved by refining the surface grains of the materials. In this paper, surface mechanical grinding (Surface mechanical attrition technology, SMAT) and supersonic particle bombardment (Supersonic fine particles bombarding,SFPB were applied to 304 stainless steel and 7A04 aluminum alloy respectively. The results show that nanocrystalline structures with a certain thickness are prepared on the surface of stainless steel and aluminum alloy respectively. In order to determine the thermal stability of the microstructure of the prepared nanocrystalline, the diffusion bonding process between surface self-nanocrystalline 304 stainless steel and 7A04 aluminum alloy was established. The nanocrystalline structures of surface self-nanocrystalline 304 stainless steel and 7A04 aluminum alloy were annealed at different temperatures, and the nanocrystalline structures of the two kinds of metals were studied by metallographic microscope and X-ray diffraction (XRD), microhardness analyzer. Finally, the microstructure and properties of the joints were analyzed by SEM, microhardness, shear strength and X-ray diffraction. The results show that nanocrystalline structures with thickness of 100 渭 m and 20 渭 m are prepared on the surface of 304 stainless steel and solution aged 7A04 aluminum alloy after surface self-nanocrystalline treatment. The grain refinement mechanism of stainless steel is mechanical twin. Dislocation motion and strain-induced martensite transformation work together, while the refinement mechanism of aluminum alloy is the result of dislocation movement. The self-nanocrystalline surface treatment not only refines the grain size, but also increases the number of grain boundaries and the density of defects in the material, which will improve the properties of the diffusion bonding joints. The thermal stability of nanocrystalline microstructure on the surface of two kinds of metals was studied. The results show that the nanocrystalline structure of 304 stainless steel has good thermal stability when the temperature is not higher than 600 鈩，

本文編號(hào)：2272267