Aluminum alloy welding difficulties and attention points knowledge

Aluminum alloy welding difficulties and attention points knowledge

Welding work is an indispensable step in aluminum alloy processing, and it is also a very critical step. If we can do this step better and more refined, the quality of this aluminum alloy product will also be very strong and reliable. However, some people in the process of aluminum alloy processing, always encounter some special problems, which are difficult to solve, resulting in the final processing of aluminum alloy is not successful. So, what are the difficulties when welding aluminum alloy? Xiaobian today to give you a simple talk.

Aluminum alloy products

1. Oxide film:

Aluminum is easily oxidized in the air and during welding, and the generated alumina (Al2O3) has a high melting point, is very stable, and is not easy to remove.

Hindering the melting and fusion of the base material, the ratio of oxide film is large, it is not easy to surface, and it is easy to produce slag inclusion, non-fusion, and non-welding penetration.

The surface oxide film of aluminum and the absorption of a large amount of water, easy to make the weld porosity.

Before welding, the surface should be strictly cleaned by chemical or mechanical methods to remove the oxide film on the surface. Strengthen protection during welding to prevent oxidation.

In argon tungsten arc welding, the AC power supply is used to remove the oxide film through the "cathode cleaning" effect. In gas welding, a flux that removes the oxide film is used.

When welding thick plates, the welding heat can be increased, for example, the helium arc heat is large, the use of helium or argon-helium mixed gas protection, or the use of large specifications of molten electrode gas protection welding, in the case of direct current connection, there is no need for "cathode cleaning".

2. High thermal conductivity

The thermal conductivity and specific heat capacity of aluminum and aluminum alloy are about twice that of carbon steel and low alloy steel.

The thermal conductivity of aluminum is more than ten times that of austenitic stainless steel.

In the welding process, a large amount of heat can be rapidly conducted to the base metal, so when welding aluminum and aluminum alloy, in addition to the energy consumed in the molten metal pool, there is more heat unnecessary consumption in other parts of the metal, the consumption of this useless energy is more significant than the welding of steel, in order to obtain high-quality welded joints, Energy concentration and power should be used as far as possible, and sometimes process measures such as preheating can be used.

3.线膨胀系数大，易变形和产生热裂纹

铝及铝合金的线膨胀系数约为碳素钢和低合金钢的两倍。铝凝固时的体积收缩率较大，焊件的变形和应力较大，因此，需采取预防焊接变形的措施。

铝焊接熔池凝固时容易产生缩孔、缩松、热裂纹及较高的内应力。生产中可采用调整焊丝成分与焊接工艺的措施防止热裂纹的产生。

在耐蚀性允许的情况下，可采用铝硅合金焊丝焊接除铝镁合金之外的铝合金。在铝硅合金中含硅0.5%时热裂倾向较大，随着硅含量增加，合金结晶温度范围变小，流动性显著提高，收缩率下降，热裂倾向也相应减小。

根据生产经验，当含硅5%~6%时可不产生热裂，因而采用SAlSi條（硅含量4.5%~6%)焊丝会有更好的抗裂性。

4.极易溶解氢

铝及铝合金在液态能溶解大量的氢，固态几乎不溶解氢。在焊接熔池凝固和快速冷却的过程中，氢来不及溢出，极易形成氢气孔。

弧柱气氛中的水分、焊接材料及母材表面氧化膜吸附的水分，都是焊缝中氢气的重要来源。

因此，对氢的来源要严格控制，以防止气孔的形成。

5.接头处和热影响区容易软化

合金元素易蒸发、烧损，使焊缝性能下降。

母材基体金属如为变形强化或固溶时效强化时，焊接热会使热影响区的强度下降。

铝为面心立方晶格，没有同素异构体，加热与冷却过程中没有相变，焊缝晶粒易粗大，不能通过相变来细化晶粒。

进行铝合金加工，我们需要格外注意的问题除了上面的哪些以外，还要注意铝合金自身的质量问题。通常在进行铝合金铸造的过程中，由于自身设备或者铝合金原料的问题，铝合金会出现一些气泡，这样的铝合金产品即使是进行焊接，它依然还是会存在一些质量问题。一件合格的铝合金产品，需要经过方方面面的检查和不断钻研的技巧。