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Last time we introduced aluminum alloy 6005A in detail, today we will continue to introduce the fillet welding experiment of aluminum alloy 6005A and the influence of external factors on welding. The experimental samples are the two most common 6005A profiles with thickness of 4mm and 10mm.The melting electrode argon arc welding process was used to weld 99.999% high-purity argon as the shielding gas, and the welding material was Orinkang ER5087 with a diameter of 1.2mm. Their detailed chemical composition is shown in the figure below.

6005A Chemical Composition

ER5087 Chemical Composition

Fillet welding parameters

Welding torch Angle

By observing the macroscopic metallographic structure, it can be seen that: the Angle of the welding gun is 40 °~ 45 °, and the welding seam is formed perfectly compared with other angles, and the fusion between the vertical plate and both sides of the bottom plate is good. When the Angle of welding gun is between 45 ° and 50 °, the fusion of welding seam bottom plate is less. When the Angle of the welding gun is greater than 50 °, a contraction groove extending into the welding seam through the fusion line will appear at the root of the welding seam. The front end of the contraction groove has a fine crack extending to the center of the weld.

Arc pointing

The arc can be pointed in one of three ways: 1 ~ 1.5mm deflected vertical plate, deflected center plate and 1 ~ 1.5mm deflected bottom plate. Generally, the 35° ~ 45° welding Angle is  to used to verify the experiment. When the arc is pointed slightly towards the vertical plate or the center of the welding toe, the root of the welding seam will appear micro cracks. When the arc is pointed slightly towards the bottom plate, the microscopic defects in the root of the weld will disappear. This is mainly because the fillet weld is a three-dimensional heat dissipation mode, while the heat conduction in two directions on the bottom plate and only in one direction on the vertical plate. When the arc is pointed towards the center of the vertical plate or the welding toe, the heat emission from the bottom plate is faster than that from the vertical plate. Because of the heat conduction in both directions, the weld pool on the bottom plate in the root part of the welding toe will be the first to condense than that in the direction of the vertical plate. However, when the arc is pointing slightly towards the bottom plate, it is not easy to have micro-cracks at the root of the welding toe. Because the condensation rate of the weld pool at the root of the weld toe is equivalent in the three-dimensional direction, the force of the weld pool is balanced in the 3D direction.

In addition, when arc pointing slightly towards the vertical plate, it will take the initiative to extend in the direction of the floor below drawing, often flashing will happen in the process. The instability of welding process is relatively large compared with other two kinds of welding methods. In the process of welding arc beat increased the risk of weld defects.

In the production of aluminum alloy high-speed train products, the fillet welding between the vertical plate and the bottom plate is often encountered. In the experiment, 4mm and 10mm Al-profiles with common thickness were selected as the bottom plate and the vertical plate respectively for welding test. The angle of welding gun and arc direction are the best parameters based on the above related test results. The results show that the weld pool dissipates heat in three directions during fillet welding, and the heat conduction velocity of the bottom plate is fast, so the cooling speed of the side of the weld pool that is inclined to the bottom plate is faster than that of the side of the weld pool that is inclined to the bottom plate because of the heat dissipation in the two directions. Due to the different cooling rates on both sides of the weld pool during the welding process, the newly formed solid weld is subjected to the tensile stress of microcracks.

In general, in the process of fillet welding of 6005A aluminum alloy, the most suitable welding gun operation is 35 ~ 45 °. In order to reduce the tendency of producing micro-cracks at the root of the fillet weld, the welding wire should be pointed slightly towards the bottom plate about the diameter distance of a wire. In addition, the thickness of the bottom plate should be larger than the vertical plate as much as possible.