Stress corrosion cracking of sensitized AA5083 (Al-4.5Mg-1.0Mn)
Stress corrosion cracking of sensitized AA5083 (Al-4.5Mg-1.0Mn)
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DOI：
10.1007/s11661-001-1036-3
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发表时间：
2001-11-01
影响因子：
2.8
通讯作者：
Buchheit, RG
中科院分区：
文献类型：
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作者：
Searles, JL;Gouma, PI;Buchheit, RG
AA 5083（Al-4.4Mg-0.7Mn-0.15Cr）合金是一种不可热处理的铝合金，以其优异的耐腐蚀性而闻名。然而，当暴露在50 ℃至200 ℃的温度下足够长的时间时，它可能对晶间应力腐蚀开裂（IGSCC）敏感。这种IGSCC被广泛认为与电化学活性β相Al 3 Mg 2的溶解有关，其沉淀在晶界上。最近，替代机制已被调用相关的氢效应和/或游离镁偏析或耗尽在晶界区域。为了建立致敏效应的基线，在开路条件下和在3.5%NaCl中对在150 degreesC下等温处理的样品进行电位控制下进行恒定延伸率测试（CERT）。为了帮助解释CERT结果，晶界沉淀和溶质耗尽的特征在于透射电子显微镜（TEM）。此外，β相的电化学行为通过以本体形式合成的金属间化合物的阳极极化来表征。In. CERT在开路条件下，测得的延展性强烈依赖于敏化时间，达到最低值在189小时，随后在较长的时间略有增加。这种趋势与β相在晶界上的分数覆盖率很好地相关，该分数覆盖率增加到189小时，其中它以几乎连续的覆盖率存在。在较长的时间内，这种膜变粗并变得不连续。相应地，对IGSCC的一些抗性被恢复。在极化实验中，发现本体合成的β相从其腐蚀电位（-1.40 V-SCE）至高达约-0.92 V-SCE是自发钝化的，其中观察到钝化被破坏。极化低于β相击穿电位的敏化AA 5083样品几乎没有显示IGSCC的证据，表明高β溶解速率是IGSCC的要求。镁贫化区观察到沿着晶界敏化合金，但在IGSCC中的溶质贫化的明确作用不能定义的基础上，在这项研究中开发的结果。
The AA5083 (Al-4.4Mg-0.7Mn-0.15Cr) alloy is a nonheat-treatable aluminum alloy known for its excellent corrosion resistance. However, it can become Susceptible to intergranular stress corrosion cracking (IGSCC) when exposed to temperatures ranging from 50 degreesC to 200 degreesC for sufficient lengths of time. This IGSCC is widely believed to be associated with dissolution of the electrochemically active beta phase, Al3Mg2, which is precipitated on grain boundaries. Recently, alternative mechanisms have been invoked related to hydrogen effects and/or free Mg segregation or depletion in the grain-boundary regions. To establish a baseline for the sensitization effect, constant-extension-rate tests (CERTs) were conducted under open-circuit conditions and under potential control in 3.5 pct NaCl on samples isothermally treated at 150 degreesC. To aid in interpreting the CERT results, grain-boundary precipitation and solute depletion were characterized by transmission electron microscopy (TEM). Additionally, the electrochemical behavior of the beta phased was characterized by anodic polarization of the intermetallic compound synthesized in bulk form. In. CERTs under open-circuit conditions, the measured ductility depended strongly on sensitization time, reaching a minimum at 189 hours, followed by a slight increase at longer times. This trend correlated well with the fractional coverage of beta phase on grain boundaries, which increased up to 189 hours, where it existed with nearly continuous coverage. At longer times, this film coarsened and became discontinuous. Correspondingly, some resistance to IGSCC was recovered. In polarization experiments, bulk synthesized beta phase was found to be spontaneously passive from its corrosion potential (-1.40 V-SCE) up to about -0.92 V-SCE, where passivity was observed to break down. Sensitized AA5083 samples polarized below the beta -phase breakdown potential showed almost no evidence of IGSCC, indicating that a high beta dissolution rate is a requirement for IGSCC. Mg-depleted zones were observed along grain boundaries in sensitized alloys, but a clear role for solute depletion in IGSCC could not be defined on the basis of the results developed in this study.