Some welding process issues that new users of titanium alloy laser welding machines often encounter.
2019-10-17
Whether it is aluminum alloy or titanium alloy laser welding, both are widely used materials in industrial production applications. Due to the concentration of energy and the small heat-affected zone of lasers, they have good welding processes, which makes them widely used in many complex welding processes, especially in smart homes, smart lock panels made of titanium alloy materials, and aircraft manufacturing, such as the F22 in the United States and China's J-20 stealth fighter jets, where titanium alloys are ubiquitous. However, due to the characteristics of titanium alloys themselves, if the process technology and welding control are not well managed during laser welding, some defects may occur. Below, I will introduce some defects that are easy to occur during the operation of titanium alloy laser welding machines, so that users can take some measures to avoid these problems.
1. Porosity issues:
Porosity is often said to be a common problem in laser welding, but it is even more likely to occur in titanium alloy laser welding. It is one of the defects that poses a significant threat to the quality of the welding process of the workpiece. Porosity occurs because it is trapped within the material of the workpiece, making it prone to stress relaxation, which affects the process level of the weld seam and the tensile strength coefficient of the weld. So what causes porosity to appear internally? It turns out that during the welding process, the convection of the molten pool's upper metal is most intense, and the protective gas may be drawn into the molten pool. Due to the extreme temperature gradient inside the molten pool, when the welding molten pool solidifies quickly, the protective gas that is drawn into the molten pool does not have time to escape, thus forming pores at the bottom of the molten pool.
In addition, the rapid solidification of the welding molten pool may also cause the photo-induced plasma in the molten pool to not have enough time to escape, solidifying simultaneously with the liquid metal in the molten pool, ultimately forming vacuum pores inside the weld.
2. Welding cracks
During titanium alloy laser welding, it is very easy to absorb nitrogen, oxygen, and hydrogen from the surrounding air, reacting with them to form interstitial solid solutions. This hinders the movement of dislocations between grain boundaries, significantly increasing the hardness of the weld seam, but reducing its plasticity, leading to embrittlement of the entire welded joint.
Hydrogen is the main cause of welding cracks that occur after the weld seam and surrounding high-temperature areas cool down.
The role of hydrogen in titanium alloys is to expand the β phase region, lower the transformation temperature of the β phase, and enhance the β phase. However, the effect of hydrogen on the overall performance of the weld seam is specifically manifested as delayed cracking in the heat-affected zone. In fact, the hydrogen content in the heat-affected zone is significantly higher than that in the fusion zone, as hydrogen is transported into the quenching layer near the molten metal due to the convection of the molten metal in the molten pool. Consequently, after cooling, a substantial amount of TiH2 precipitates in the heat-affected zone, resulting in increased brittleness.
Additionally, titanium alloys have relatively low thermal conductivity, and the welding molten pool continuously transfers heat to the heat-affected zone through thermal conduction, keeping the heat-affected zone at a high temperature. This causes the precipitated hydrides to expand rapidly, resulting in significant local stress. When the local stress exceeds the yield limit of the material, cracks will occur.
From the above description, we can see that titanium alloy laser welding is prone to two major defects: porosity and cracks. Such welding technology requires experienced welders to avoid these issues in practical operations. How to use it to avoid these shortcomings? You can consult our SHINHOP laser welding technology engineers. If you are not well-informed about laser welding equipment during product equipment procurement or do not have a deep understanding of the characteristics of welding materials, you are always welcome to come to our SHINHOP laser equipment company's welding engineering department for communication and cooperation.
[This article is written by "SHINHOP Laser Equipment". Some content comes from the internet and is for reference and learning only. Reproduction/copying is not allowed to avoid unnecessary legal liability issues.]
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Shenzhen SHINHOP Laser Equipment Co., Ltd. It is a scientific and technological enterprise specializing in the research and development, production and sales of industrial laser processing equipment. It has been deeply engaged in the new energy industry for 20 years, focusing on the non-standard customization of automatic lithium battery cell assembly line and module PACK production line. It has successively obtained the national high-tech and specialized new enterprise certification.
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