During production, the following measures can be taken to prevent welding hot cracks of aluminum and aluminum alloy:

1. Select masterbatch with small hot crack tendency, and strictly control impurity content

Various aluminum alloys have different tendency to weld hot cracks. Among them, industrial pure aluminum and rust proof aluminum have less tendency of hot cracking. However, when the mass fraction of Mg in Al Mg alloy is 2%~3%, the hot cracking tendency is also large. Generally speaking, the hot cracking tendency of heat treatment strengthened aluminum alloys is relatively large. Therefore, rust proof aluminum, 2A16 (LY16) and Al Zn Mg alloy are mostly used as welding structures; The second is 6A02 (LD2), 2A14 (LD10), 2A11 (LY11) alloy; 2A12 (LY12) and 7A04 (LC4) alloys are mainly used for resistance welding structures.

2. Correct selection of filler metal

When the base metal is determined, the correct selection of filler material is the key to prevent hot cracking. In general, filler metal can play a role in preventing hot cracks from the following aspects:

① Increasing the amount of low melting point eutectic plays a "self-healing" role on cracks.

For example, for some duralumin alloys with high hot crack tendency, it is difficult to adjust the weld composition in the original alloy system, but if ω Si5% Al Si welding wire (SAlSi5) can form more low melting point eutectic, which can "self heal", so it has a high resistance to hot cracks.

② The weld shall be modified.

Almost all aluminum alloy welding wires contain Ti, Zr, V, B and other trace elements, which are generally added as modifiers. These elements can form fine particles of refractory intermetallic compounds with Al, and play the role of non spontaneous crystallization core, so they can refine grains, evacuate low melting point eutectic, and improve the hot cracking resistance of welds.

③ Reduce the effective crystallization temperature range.

For example, the B61 welding wire developed for welding Al Cu Mg series duralumin is added with Ni, Mn and Ti elements. Ni can peritectic react with Al and Cu to form complex intermetallic compounds (CuAlNi), which can increase the solidus temperature, thus reducing the effective crystallization temperature range. In addition, Mn and Ti can refine the grains, thus improving the hot cracking resistance of the weld.

3. Correct selection of welding methods and parameters

The welding method of heat energy concentration can realize rapid welding and prevent the formation of thick columnar crystals with strong directivity, so it can reduce the tendency of hot cracks. For example, the tendency of hot cracks in TIG or MIG welding is much smaller than that in gas welding.

In the selection of welding parameters, smaller welding current and slower welding speed should be selected. Because too much current will not only overheat the molten pool and coarsen the columnar crystal, but also increase the fusion ratio, so that the base metal with a greater tendency to hot cracks will enter the weld too much, thus increasing the tendency to hot cracks; If the welding speed is too fast, the strain rate of the weld during the crystallization process will be increased, and the tendency of hot cracks will also be increased.

What preparations should be made for aluminum and aluminum alloy welding?

⑴ The purpose of pre welding cleaning is to remove the oxide film and oil stain on the surface of the weldment, which is an important measure to prevent the generation of pores and slag inclusion.

A. Chemical cleaning has high efficiency and stable quality, and is suitable for cleaning welding wires and weldments of small size and mass production. There are two kinds of chemical cleaning methods: immersion cleaning method and scrubbing method, cleaning agent and cleaning process

B For mechanical cleaning, firstly use organic solvent (acetone, rosin or gasoline) to wipe the oil stain on the surface of the weldment, and then use a fine copper wire to brush the surface to expose metal luster, or use a scraper to clean the surface. The cleaned weldment shall be welded within 4h, otherwise it shall be cleaned again.

(2) In order to ensure the penetration of welding and prevent the weldment from penetration or collapse, the base plate can be placed under the joint before welding. The backing plate can be made of graphite, stainless steel or carbon steel, with an arc groove on the surface to ensure the formation of the reverse weld. (3) Preheating is generally not required for thin and small weldments. When welding weldments with a thickness of more than 5 mm, the weldments shall be preheated at 100~300 ℃ before welding in order to reach the required temperature near the joint.

What cleaning work should be done after aluminum and aluminum alloy welding?

The residual flux and welding slag left in the weld and adjacent to the weldment after welding shall be cleaned in time, otherwise, under the action of air and water, the residual solvent and welding slag will damage the aluminum oxide film with anti-corrosion effect and severely corrode the weldment. Therefore, the residual dirt on the weldment shall be strictly removed immediately after welding.

Source: Welding technology

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