【摘要】：鋁及鋁合金具有密度低、導(dǎo)電導(dǎo)熱性好等優(yōu)點(diǎn),工業(yè)應(yīng)用廣泛。本文采用7075鋁合金為研究材料,該材料是高速發(fā)展的航天航空產(chǎn)業(yè)以及船舶行業(yè)新型鋁材。然而,沿海地區(qū)的飛機(jī)與船艦的服役環(huán)境復(fù)雜多變,海水中氯離子的存在是對金屬材料的一大威脅,因此本文圍繞7075鋁合金在海洋環(huán)境中的腐蝕行為機(jī)理進(jìn)行研究,結(jié)果如下:通過研究鹽度對7075鋁合金耐腐蝕性能的影響,獲得該合金的腐蝕機(jī)理,研究結(jié)果表明:鹽度增加致使Cl-對金屬基體破壞加劇,合金表面逐漸出現(xiàn)微小孔洞,腐蝕電位正移,彌散指數(shù)降低,電極表面粗糙度增加,耐腐蝕性能下降。NaCl溶液中存在強(qiáng)活化作用的Cl-,7075鋁合金腐蝕產(chǎn)物Al(OH)3的OH-逐漸被Cl-取代,合金表面氧化膜不斷損壞,新的腐蝕產(chǎn)物AlCl3形成。在0.6 mol/LNaCl溶液中,室溫環(huán)境,通過HCl與NaOH調(diào)節(jié)溶液p H值,研究7075鋁合金在不同pH值條件下的耐腐蝕性能,研究結(jié)果表明:pH3~7,電荷傳遞電阻升高,電荷傳遞受阻,耐腐蝕性能增大。pH9~11,電極表面氧化膜穩(wěn)定性降低,阻擋層溶解過程加快,腐蝕速度從0.0914 mm/a增加到2.1222mm/a,腐蝕加劇。強(qiáng)酸溶液中,電化學(xué)阻抗譜中感抗弧明顯,存在不均勻點(diǎn)蝕。pH=7、9時(shí),電化學(xué)阻抗譜中只出現(xiàn)1個(gè)容抗弧,為鋁合金基體溶解過程。pH=11時(shí),7075鋁合金電化學(xué)腐蝕行為存在兩個(gè)過程:阻擋層生成附著過程和阻擋層溶解反應(yīng)過程。在掃描電鏡(SEM)的基礎(chǔ)上運(yùn)用新型探針掃描技術(shù)掃描電化學(xué)顯微鏡(SECM)觀測7075鋁合金在0.6 mol/LNaCl溶液中浸泡腐蝕的表面形貌,研究結(jié)果表明:浸泡初期7075鋁合金以點(diǎn)腐蝕為主,浸泡時(shí)間延長,金屬基體逐漸溶解,溶液Al3+濃度增大,合金表面出現(xiàn)細(xì)小坑點(diǎn),坑點(diǎn)分布稀疏,表面層狀結(jié)構(gòu)消失。在0.6 mol/LNaCl溶液中,7075鋁合金中ZnAl相和ZnAlMg相腐蝕電位較高,與基體形成腐蝕微電解池,作陰極,腐蝕電位較低的鋁基體作陽極,導(dǎo)致ZnAl相和ZnAlMg相周圍的鋁陽極溶解。
[Abstract]:Aluminum and aluminum alloys have the advantages of low density, good conductivity and thermal conductivity, so they are widely used in industry. In this paper, 7075 aluminum alloy is used as the research material, which is a new type of aluminum material in aerospace industry and ship industry. However, the service environment of aircraft and ships in coastal areas is complex and changeable, and the presence of chlorine ions in sea water is a great threat to metal materials. Therefore, the corrosion mechanism of 7075 aluminum alloy in marine environment is studied in this paper. The results are as follows: by studying the effect of salinity on corrosion resistance of 7075 aluminum alloy, the corrosion mechanism of 7075 aluminum alloy is obtained. The corrosion potential shifted positively, the dispersion index decreased, the surface roughness of the electrode increased, and the corrosion resistance decreased. The OH- of Al (OH) 3, a corrosion product of Cl-,7075 aluminum alloy with strong activation in NaCl solution, was gradually replaced by Cl-. The oxide film on the surface of the alloy is continuously damaged, and a new corrosion product, AlCl3, is formed. The corrosion resistance of 7075 aluminum alloy under different pH values was studied by adjusting pH value of 7075 aluminum alloy in 0. 6 mol/LNaCl solution at room temperature by HCl and NaOH. The results showed that the charge transfer resistance of pH3~7, was increased and the charge transfer was blocked. The stability of the oxide film on the surface of pH9~11, electrode is decreased, the dissolution process of the barrier layer is accelerated, and the corrosion rate is increased from 0.0914 mm/a to 2.122 mm / a. In the strong acid solution, the inductive arc is obvious in the electrochemical impedance spectrum, and there is inhomogeneous pitting corrosion. At pH=7, 9, there is only one capacitive arc in the electrochemical impedance spectrum, which is the dissolution process of aluminum alloy matrix. PH= 11:00, The electrochemical corrosion behavior of 7075 aluminum alloy has two processes: the formation of barrier layer adhesion process and the barrier layer dissolution reaction process. On the basis of scanning electron microscope (SEM), scanning electrochemical microscope (SECM) was used to observe the surface morphology of 7075 aluminum alloy immersed in 0.6 mol/LNaCl solution by scanning electrochemical microscope (SECM). The results show that the corrosion of 7075 aluminum alloy is mainly pitting corrosion at the beginning of soaking, the immersion time is prolonged, the metal matrix dissolves gradually, the concentration of Al3 in the solution increases, the surface of the alloy appears small pits, the distribution of the pits is sparse, and the layered structure of the surface disappears. In 0. 6 mol/LNaCl solution, the corrosion potential of ZnAl phase and ZnAlMg phase in 7075 aluminum alloy is higher. The corrosion microelectrolysis cell is formed with the substrate as cathode, and the aluminum substrate with lower corrosion potential is used as anode, which leads to the dissolution of aluminum anode around ZnAl phase and ZnAlMg phase.
【學(xué)位授予單位】：江西理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG178

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