![]() This can provide a weld with excellent crack resistance and a solidification temperature a little lower than the base alloy. Often welded autogenously (without filler alloy), these alloys are easy to weld with a filler alloy that has slightly more Mg than the base alloy. The majority of the 5xxx base alloys, which contain around 5% Mg, show low crack sensitivity. When considering the welding of the more commonly used 5xxx series (Al-Mg) and the 6xxx series (Al-Mg-Si) aluminum base alloys, these principals are clearly illustrated. Second, when welding base alloys that have high crack sensitivity, use a filler alloy with a different chemistry than that of the base alloy to create a weld metal chemistry that has low crack sensitivity. First, when welding base alloys that have low crack sensitivity, always use a filler alloy of similar chemistry. With the knowledge of the importance of chemistry on crack sensitivity of an aluminum weld, two fundamental principals apply that can reduce the incidence for hot cracking. ![]() Utilizing the same principals, it can be concluded that the crack sensitivity of an aluminum weld, which is generally comprised of both base alloy and filler alloy, is also dependent on its chemistry. ![]() Additionally, the figure shows alloys that display low cracking characteristics have chemistries well away from the crack sensitivity peaks.īased on these facts, it is clear that crack sensitivity of an aluminum base alloy is primarily dependent on its chemistry. After studying the crack sensitivity curves, it is easy to recognize that most of the aluminum base alloys considered unweldable autogenously (without filler alloy addition) have chemistries at or near the peaks of crack sensitivity. The crack sensitivity curves (Fig 1) reveal that with the addition of small amounts of alloying elements, the crack sensitivity becomes more severe, reaches a maximum, and then falls off to relatively low levels. The diagram shows the effects of four different alloy additions - Silicon (Si), Copper (Cu), Magnesium (Mg) and Magnesium Silicide (Mg2Si) - on the crack sensitivity of aluminum. The aluminum crack sensitivity curves (Fig 1) is a helpful tool in understanding why aluminum welds crack and how the choice of filler alloy and joint design can influence crack sensitivity. They are susceptible base alloy chemistry, selection and use of the most appropriate filler alloy and choosing the most appropriate joint design. There are three areas that can significantly influence the probability for hot cracking in an aluminum welded structure. This cracking mechanism is also known as hot shortness, hot fissuring, solidification cracking and liquation cracking. Hot cracking is a high-temperature cracking mechanism and is mainly a function of how metal alloy systems solidify. Hot cracking is the cause of almost all cracking in aluminum weldments. However, when welding aluminum alloys hydrogen cracking cannot occur. Hydrogen cracking is often a major concern when welding carbon steels and high strength low alloy steels. One of the most notorious is hydrogen cracking, also referred to as cold cracking. There are a number of cracking mechanisms associated with the welding of metallic alloys. The primary cracking mechanism in aluminum welds Having this advance knowledge will help avoid cracking situations. In order to appreciate the potential for problems associated with cracking, it is necessary to understand the many different aluminum alloys and their various characteristics. The majority of aluminum base alloys can be successfully arc welded without cracking related problems, however, using the most appropriate filler alloy and conducting the welding operation with an appropriately developed and tested welding procedure is significant to success.
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