PORE FORMATION IN WELDED JOINTS OF Al-Mg-Li ALUMINUM ALLOY WHEN WELDED WITH AMg-6 ADDITIVE WIRE
Aluminum alloys of the Al-Mg-Li alloying system are widely used in aircraft construction due to their properties. The main difficulty in welding aluminum alloys is related to the formation of pores. This paper presents metallographic studies of pores in welded joints of aluminum alloy obtained by argon-arc welding with AMg-6 filler wire. The analysis was carried out under different illumination in order to correctly identify the pores, their location and shape. If in the light field it is quite difficult to distinguish pores from inclusions, then with gradual extinguishing: from the light field, to the polarized light and dark field, it is possible to observe their clear glow in the aureole. According to the results of the research, it was found that pores in welded joints are present in different areas of the weld. Their primary location was revealed along the alloying line and along the boundaries of the weld layers. The pores have different shapes and sizes. Their distribution varies from single pores to clusters up to 4-5 per 1 cm. Since hydrogen is considered to be the main cause of pore formation in welded joints of aluminum alloys, the reasons of its impact on pore formation were analyzed. On the basis of literature data and the results obtained, it was found that during cooling of the weld pool, hydrogen, redistributing into molecules, forms gas bubbles. The formed bubbles, due to changes in solubility, float up. This process occurs as long as the viscosity of the surrounding metal allows. In addition, it has been revealed that welded joints have a rather extended fusion zone during argon-arc welding, and the magnesium content will reduce hydrogen diffusion and metal viscosity, which makes it difficult for gas bubbles to pop up after metal crystallization, leading to porosity formation.