Partially-Melted-Zone Cracking in Aluminum Welds

铝焊缝中的部分熔化区裂纹

• 批准号: 0098776
• 负责人: Sindo Kou
• 金额: $ 29.91万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-07-01 至 2005-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0098776&HistoricalAwards=false
• 关键词: Partially; Melted; Zone; Cracking; Aluminum

0098776KouAluminum alloys are susceptible to hot cracking in the region right outside the fusion zone called the partially melted zone (PMZ), where grain boundary liquation occurs during welding. Studies on 6000 alloys (Al with Mg, Si and some Cu, Cr and Fe) have demonstrated that the composition of the weld metal is critical in preventing PMZ cracking. It has been proposed that cracking occurs if the weld metal composition is such that TWS (the weld metal solidus temperature) TBS (the base metal solidus temperature). However, contradictions to this TWS TBS criterion for cracking have been reported possibly because of inaccurate TWS and TBS and/or non-equilibrium solidification. This collaborated study between UW-Madison and ALCOA on PMZ cracking in aluminum welds focuses on the mechanism of cracking and the effect of the weld metal composition. First, the PMZ microstructure of several aluminum alloys will be observed to prove that the solidifying and shrinking weld metal pulls and tears the liquated PMZ to cause cracking. Second, binary and ternary alloys of known TWS and TBS will be prepared and welded to test the TWS TBS criterion for cracking. Al-4.5Cu alloy will be welded with pure Al (TWS TBS) and Al-6.3Cu (TWS TBS) fillers, and the resultant welds will be checked for PMZ cracking. Likewise, Al-1Mg-0.6Si alloy (close to the popular alloy 6061, which is being used for car frames) will be welded with pure Al (TWS TBS), Al-5.2Si (TWS TBS) and Al-5Mg (TWS TBS) fillers and checked. Third, the feasibility of assessing the PMZ cracking susceptibility with non-equilibrium T (temperature) vs. fs (fraction of solid) curves will be checked with the welds of the binary and ternary alloys. TWS and TBS reflect equilibrium solidification but non-equilibrium solidification prevails in welding. A PMZ higher in fs than the weld metal at any T is likely to be stronger than the weld metal, resisting its pulling and tearing. T vs. fs will be calculated using a computer code developed at UW-Madison based on thermodynamic and kinetic models and tested extensively with aluminum alloys. %%%As the auto industry is moving to all-aluminum cars, it is essential to better understand and control defects in aluminum welds. ALCOA has a strong interest in hot cracking in aluminum alloys and will cast the binary and ternary alloys for UW-Madison. Graduate students will go to ALCOA to learn how to cast special alloys for welding and duplicate the ALCOA facility at UW-Madison. ***

0098776 Kou铝合金在熔合区外的部分熔化区（PMZ）容易发生热裂纹，在焊接过程中会发生晶界液化。对6000合金（含Mg、Si和一些Cu、Cr和Fe的Al）的研究表明，焊缝金属的成分对防止PMZ裂纹至关重要。已经提出，如果焊缝金属成分使得TWS（焊缝金属固相线温度）TBS（基底金属固相线温度），则发生裂纹。然而，矛盾的TWS TBS开裂标准已被报道可能是因为不准确的TWS和TBS和/或非平衡凝固。UW-Madison和ALCOA之间关于铝焊缝PMZ开裂的合作研究侧重于开裂机制和焊缝金属成分的影响。首先，将观察几种铝合金的PMZ显微组织，以证明凝固和收缩的焊缝金属拉伸和撕裂液化PMZ导致开裂。其次，将制备和焊接已知TWS和TBS的二元和三元合金，以测试TWS TBS开裂标准。Al-4.5Cu合金将使用纯Al（TWS TBS）和Al-6.3Cu（TWS TBS）填料进行焊接，并将检查所得焊缝是否存在PMZ裂纹。同样，Al-1 Mg-0.6Si合金（接近用于汽车车架的流行合金6061）将与纯Al（TWS TBS）、Al-5.2Si（TWS TBS）和Al-5 Mg（TWS TBS）填料焊接并检查。第三，评估的PMZ裂纹敏感性与非平衡T（温度）与fs（固体分数）曲线的可行性将检查与焊缝的二元和三元合金。TWS和TBS反映了平衡凝固，但在焊接中以非平衡凝固为主。在任何温度下，fs比焊缝金属高的PMZ可能比焊缝金属更强，从而抵抗其拉伸和撕裂。T与fs的关系将使用威斯康星大学麦迪逊分校开发的基于热力学和动力学模型的计算机代码进行计算，并使用铝合金进行广泛测试。%随着汽车工业向全铝汽车发展，更好地了解和控制铝焊缝中的缺陷至关重要。ALCOA对铝合金的热裂纹有浓厚的兴趣，并将为威斯康星大学麦迪逊分校铸造二元和三元合金。研究生将去ALCOA学习如何铸造特殊合金焊接和复制在威斯康星大学麦迪逊分校的ALCOA设施。***