1.1 该测试方法也称为硝酸质量损失测试(NAMLT)，涵盖了5XXX系列铝合金的恒定浸没晶间腐蚀测试程序。 1.2 本试验方法仅适用于锻造产品。 1.3 本试验方法包括试样类型、试样制备、试验环境和暴露方法。 1.4 以SI单位表示的值应被视为标准。括号中给出的值仅供参考。 1.5 本标准并不旨在解决与其使用相关的所有安全性问题（如果有）。本标准的使用者有责任在使用前建立适当的安全、健康和环境实践并确定法规限制的适用性。 1.6 本国际标准是根据Guid关于制定国际标准的原则的决定中确立的国际公认的标准化原则制定的世界贸易组织技术性贸易壁垒（TBT）委员会发布的es和建议。 ======意义和用途====== 5.1 该试验方法提供了Al-Mg和Al-Mg-Mn合金晶间腐蚀敏感性的定量测量。硝酸优先于镁在铝基质中的固溶体溶解第二相，即铝-镁金属间化合物(β Al-Mg)。当这种化合物沿着晶界以相对连续的网络沉淀时，优先攻击的效果是腐蚀晶粒周围，导致它们从样品上脱落。这种从晶粒中的脱落导致大约25mg/cm的相对较大的质量损失 2 至75 mg/cm 2 （160毫克/英寸。 2 至480毫克/英寸。 2 ），而晶间样品-抗性材料仅损失约1 mg/cm 2 至15 mg/cm 2 （10毫克/英寸。 2 至100毫克/英寸。 2 ).当β Al-Mg化合物随机分布时，优先攻击会导致中间质量损失。在这种情况下，需要进行金相检查，以确定质量损失是否是晶间侵蚀的结果。 5.2 当材料暴露于含氯化物的自然环境，例如海岸大气或海水时，晶界中第二相的沉淀也引起晶间腐蚀。合金易受晶间腐蚀的程度取决于晶界中沉淀物连续性的程度。侵蚀的可见表现可以是各种形式，如点蚀、剥落或应力腐蚀开裂，这取决于晶粒结构的形态和持续拉伸应力的存在。 3

1.1 This test method, also known as the Nitric Acid Mass Loss Test (NAMLT), covers a procedure for constant immersion intergranular corrosion testing of 5XXX series aluminum alloys. 1.2 This test method is applicable only to wrought products. 1.3 This test method covers type of specimen, specimen preparation, test environment, and method of exposure. 1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only. 1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 5.1 This test method provides a quantitative measure of the susceptibility to intergranular corrosion of Al-Mg and Al-Mg-Mn alloys. The nitric acid dissolves a second phase, an aluminum-magnesium intermetallic compound (βAl-Mg), in preference to the solid solution of magnesium in the aluminum matrix. When this compound is precipitated in a relatively continuous network along grain boundaries, the effect of the preferential attack is to corrode around the grains, causing them to fall away from the specimens. Such dropping out of the grains causes relatively large mass losses of the order of 25 mg/cm 2 to 75 mg/cm 2 (160 mg/in. 2 to 480 mg/in. 2 ), whereas, samples of intergranular-resistant materials lose only about 1 mg/cm 2 to 15 mg/cm 2 (10 mg/in. 2 to 100 mg/in. 2 ). When the βAl-Mg compound is randomly distributed, the preferential attack can result in intermediate mass losses. Metallographic examination is required in such cases to establish whether or not the loss in mass is the result of intergranular attack. 5.2 The precipitation of the second phase in the grain boundaries also gives rise to intergranular corrosion when the material is exposed to chloride-containing natural environments, such as seacoast atmospheres or sea water. The extent to which the alloy will be susceptible to intergranular corrosion depends upon the degree of precipitate continuity in the grain boundaries. Visible manifestations of the attack may be in various forms such as pitting, exfoliation, or stress-corrosion cracking, depending upon the morphology of the grain structure and the presence of sustained tensile stress. 3