【作者】 李永刚；

【导师】 卫英慧；

【作者基本信息】 太原理工大学 ， 材料加工工程， 2010， 硕士

【摘要】 随着镁合金越来越多的应用于工业生产以及日常生活,它的特性也越来越受到人们的重视,各国都投入巨额资金进行研究,研究重点有两个方面一是塑性的改善,二是耐蚀性的提高。国内外学者对镁铝合金耐蚀性的研究主要集中在大气腐蚀、溶液浸蚀两部分,在溶液浸蚀方面主要研究合金在各种溶液中的腐蚀机理,对于镁合金在盐雾条件的腐蚀行为报道较少,而AZ系镁合金又是目前应用最多的镁合金,因此有必要研究AZ系镁合金的盐雾腐蚀行为。在AZ系镁合金中β-Mg17Al12是合金中最主要的第二相,它的体积分数、形态、分布情况等极大的影响着镁合金的腐蚀行为,对Mg17Al12单相合金性能的研究会有助于对镁合金腐蚀行为的理解。镁合金的耐蚀性差,本文采用表面涂装的方法来提高薄壁压铸AZ91D镁合金的耐蚀性,探索一种配方简单的有机涂层。利用XRD、SEM、DSC、电化学工作站等仪器对试样性能进行表征,并分析了试验结果之间的相互关系,通过研究得到以下结论:1.在48h小时试验范围内三种铸态镁合金的失重率顺序为:AZ91D>AZ61A>AZ31B。2. Al含量的不同导致了腐蚀形貌的不同,在腐蚀过程中β相和α相构成的微电偶是电化学腐蚀进行的主要动力,β相能改变腐蚀前进的方向而对腐蚀进程的延缓作用较小。3.腐蚀产物主要是Mg(OH)2,经过48h腐蚀后由XRD检测表明腐蚀产物中含有水合物Mg6Al2(OH)18·5H2O。4.铸态单相Mg17Al12密度低,为2.0 g/cm3,硬度在220HV以上。5.铸态单相Mg17Al12自腐蚀电位在-1.0V,在所测试的AZ系镁合金中最高。6.氢致开裂是铸态单相Mg17Al12在NaCl溶液中裂纹形成的主导因素。7.在试验范围内对压铸AZ91D进行磷化处理的最佳温度为50℃时间为1min。8.阻抗测试表明涂装后试样的电阻在109?,涂装后比未处理试样自腐蚀电流密度降低3个数量级。9.浸蚀试验表明涂装后的试样分别在10%的H2SO4,10%的NaOH,丙酮中浸泡10天漆膜均无变化。在100℃水中浸泡72h漆膜无变化。划格试验表明漆膜和基体结合力良好,评定为0级。更多还原

【Abstract】 Along with the more and more magnesium alloys used in the industrial production and daily life, The property of magnesium alloys have been pay more attention to. Many countries are investing whopping on research. The research emphasis on two points, one is plastic improvement and another one is enhance the corrosion resistance by scholars at home and abroad. The key points of research are focus on atmospheric corrosion and immersion erosion. The major study of immersion test is the corrosion mechanism of magnesium alloy in different solutions, and the report about corrosion mechanism of magnesium alloy in severe environment such as salt spray test is little. The most applied magnesium alloy is AZ series alloy at present so we should have to understand its corrosion behavior in salt spray environment.β-Mg17Al12 is the most important second phase in AZ series alloy which volume fraction, morphology and distribution situation in the alloy that play an important role affect the corrosion behavior. The research on the single phaseβ-Mg17Al12 will be a beneficial assistance for understanding the corrosion mechanism of magnesium alloy. Magnesium alloy has low corrosion resistance, surface coating was used to improve the corrosion resistance of thin-walled die cast AZ91D magnesium alloy in this paper. The aim is to explore a simple composition organic coating. The property of specimen was characterized by XRD, SEM, DSC , Electrochemical workstation, etc, and analyzed the relationship between them. The following results were obtained:1. In the 48 hours’test range ,the weight loss rates sequence of three cast alloy as follow: AZ91D>AZ61A>AZ31B2. Different aluminum content result in the difference corrosion morphology. Micro-galvanic consists ofβphase andαphase is the main force in the corrosion process.βphase can change the direction of corrosion take place but the retardation effect on corrosion process is weak.3. The main corrosion product is Mg(OH)2. Magnesium-aluminum hydrate was detected after 48h corrosion process, XRD test show the hydrate is Mg6Al2(OH)18·5H2O.4. The density of single phase Mg17Al12 is low at 2.0/cm3 and the hardness is high more than 220HV.5. The corrosion potential of single phase Mg17Al12 is -1.0V which higher than all the AZ series alloy.6. The dominant factor of resulted in crack formation of single phase Mg17Al12 in NaCl solutions is hydrogen induced cracking.7. In test range the optimum temperature of phosphating for die cast AZ91D is 50℃and time is 1 min. 8. The impedance measurement show the electrical resistance of organic coating is 109?. The corrosion current density of sample with organic coating is lower 3 orders of magnitude than the bare sample.9. The immersion test show that organic coatings are unchanged after 10 days erosion in 10% H2SO4 , 10% NaOH and acet. The organic coatings unchanged in boiling water after 72h immersion test. The adhesion between coating and substrate is 0 grade through cross cut test.更多还原