Analysis of the reasons for the formation of aluminum alloy die-casting welding pores?

Aluminum alloy die-casting products are mainly used in electronics, automobiles, motors, home appliances and some communication industries. Some high-quality aluminum alloy products with high performance, high precision and high toughness are also used in large aircraft, ships and other industries with relatively high requirements. . The main use is still on the parts of some instruments.

When aluminum alloy die-casting is welded, the type of pores generated by welded joints is mainly hydrogen pores. The reason for the generation of hydrogen holes is that during welding, the welding material and the base metal at the welding joint are melted at high temperature to form a molten pool. Due to the extremely high temperature of the molten pool formed by these molten metals, the solubility of hydrogen increases sharply with the temperature. A large amount of hydrogen is dissolved.

When the arc leaves, the temperature of the molten pool decreases rapidly. At this time, the solubility of hydrogen decreases sharply with the decrease in temperature, and a large amount of hydrogen overflows. However, due to the relatively high crystallization speed of aluminum and the small density of aluminum alloy, the formed bubbles are The buoyancy in the molten pool is small, and the floating speed is slow. After the crystallization of the molten pool, there will be many bubbles too late to float and stay in the weld to form pores.

During the welding of aluminum alloys, hydrogen can mainly enter the weld through the welding environment, the purity of the shielding gas, the welding base material, the selection of the welding wire and the formulation of the welding process parameters. Stomatal defects can be excluded from the influence of welding process parameters. Therefore, the following related experiments will be carried out for other factors, as follows.

1 Grinding amount of base metal surface before welding

In order to determine whether the grinding amount on the surface of the base metal before welding is the cause of the porosity in the weld, the die-casting aluminum alloy was welded according to the grinding amount in Table 3. The process parameters were MIG welding, filler material ER5356, welding current 80A ~ 100A, welding speed 8mm/s ~ 12mm/s, protective gas flow 18L /min ~ 22L /min. Visual inspection, penetration and low magnification inspection were carried out on the weld. As shown in Figure 3, there are porosity defects in the die-casting aluminum alloy after welding with different grinding amounts, indicating that the grinding amount on the surface of the base metal before welding has little effect on the welding porosity of the die-casting aluminum alloy. .

2 different wires

ER4043 and ER5183 welding wires were used for testing, different process parameters were selected for welding, MIG welding, the filler materials were ER4043 and ER5183 respectively, the welding current was 60A ~ 80A, the welding speed was 8mm/s ~ 12mm/s, and the protective gas flow rate was 18L /min ~ 22L /min. After visual inspection, penetration, and internal inspection of the weld height after grinding, the inspection results are shown in Figure 4. It is found that under different process parameters, the die-casting aluminum alloy welding seam has porosity defects like the ER5356 welding wire. It shows that different welding wires will not avoid the generation of weld pores.

In order to further confirm whether the welding wire is the cause of the porosity in the weld, the die-casting aluminum alloy TIG self-fusion welding test was carried out. The process parameters are shown in Table 4, and the quality after welding is shown in Figure 5. There are a lot of pores in the welding seam, so it shows that the use of welding wire has little effect on the porosity of die-casting aluminum alloy welding.

3 Welding base metal test

In order to determine whether the welding base metal is the cause of the welding porosity, the extruded profile 6005A and the gravity cast aluminum alloy were selected for the comparative test, and the welding test was carried out in the same welding environment, using the same welding equipment and welding method, as follows:

6005A profile butt welding, 6005A profile + die-casting aluminum alloy butt welding and gravity-casting aluminum alloy butt welding were carried out, and compared with die-casting aluminum alloy butt welding; the process parameters were MIG welding, welding wire ER5356, welding current 70A ~ 100A, welding speed 8mm /s ~ 12mm/s, protective gas flow 18L /min ~ 22L /min.

After visual inspection and internal inspection after residual height grinding, there are a lot of pores in the butt weld of die-casting aluminum alloy; there are no pores in the butt joint of the profile; there are pores in the butt joint of the die-casting aluminum alloy and the profile, but the pores are all on the side of the die-casting aluminum alloy.

Through visual inspection, penetration, radiography and low magnification inspection, although there are pores in the welding seam of gravity cast aluminum alloy, the small size can be judged as qualified pores. This shows that the poor weldability of the die-cast aluminum alloy base metal is the main reason for the generation of welding pores.

4 Hydrogen content detection

Since the main component of aluminum weld pores is hydrogen, the main three carriers of hydrogen in the welding process are protective gas, base metal and welding wire. According to the above test results, the same shielding gas was used in the welding test, and different welding wires were selected at the same time, but the welding pores still existed. Therefore, the hydrogen affecting the welding pores in this test mainly came from the hydrogen content of the die-casting aluminum alloy base metal.

In order to clarify the hydrogen content of die-casting aluminum alloys, the test materials of die-casting aluminum alloys, extruded profiles, and gravity-casting aluminum alloys were selected for hydrogen content testing. The testing standards were implemented in accordance with Q/6S 2453-2010. , indicating that the hydrogen content of die-casting aluminum alloys is much higher than that of extruded profiles and gravity-casting aluminum alloys.

in conclusion

(1) Under the same welding environment, other welding factors such as changing the welding process parameters, the amount of surface grinding of the base metal before welding, and the selection of welding wires are not the main reasons for the generation of welding pores in die-casting aluminum alloys, but mainly depend on the base metal of die-casting aluminum alloys.

(2) The hydrogen content of die-casting aluminum alloy base material is higher than that of gravity-casting aluminum alloy and extruded aluminum alloy, and its welding porosity is much larger than that of gravity-casting aluminum alloy and extruded aluminum alloy, which is the main reason for the formation of welding pores.

(3) The degree of porosity tendency of aluminum alloy welding mainly depends on the hydrogen content of the base metal. With the increase of the hydrogen content of the base metal, the porosity tendency increases.