According to the difference of main alloying elements, there are four types of cast aluminum alloys.

(1) Al-Si alloy, also called "Si-Al-Ming" or "Si-Al-Ming". It has good casting performance and wear resistance, and the thermal expansion coefficient is small. Among the cast aluminum alloys, the silicon content is 10% ~ 25%. Sometimes 0.2% ~ 0.6% magnesium is added to silicon-aluminum alloy, which is widely used in structural parts, such as shells, cylinders, boxes and frames. Sometimes adding proper amount of copper and magnesium can improve the mechanical properties and heat resistance of the alloy. This kind of alloy is widely used to manufacture parts such as pistons.

(2) Al-Cu alloy, the alloy containing 4.5% ~ 5.3% Cu has the best strengthening effect. Proper addition of Mn and Ti can significantly improve the strength and castability at room temperature and high temperature. It is mainly used to manufacture sand castings with large dynamic and static loads and uncomplicated shapes.

(3) Al-Mg alloy, the casting aluminum alloy with the lowest density (2.55g/cm3) and the highest strength (about 355MPa), contains 12% Mg, and has the best strengthening effect. The alloy has good corrosion resistance in atmosphere and seawater, and has good comprehensive mechanical properties and machinability at room temperature. It can be used as radar base, engine case of aircraft, propeller, landing gear and other parts, and can also be used as decorative materials.

(4) Al-Zn alloy, in order to improve the performance, Si and Mg are often added, which is often called "Zn-Si-Al-Ming". Under the casting condition, the alloy has quenching effect, that is, "self-quenching". It can be used without heat treatment, and after heat treatment, the casting has higher strength. After stabilization, the size is stable, and it is often used to manufacture models, templates and equipment supports.

Cast aluminum alloy has the same alloy system and the same strengthening mechanism as wrought aluminum alloy (except strain strengthening). Their main difference is that the maximum content of alloying element silicon in cast aluminum alloy exceeds that in most wrought aluminum alloys. In addition to strengthening elements, the cast aluminum alloy must also contain enough eutectic elements (usually silicon) to make the alloy have considerable mobility and easily fill the shrinkage joint of the casting. At present, the basic alloys only need the following six categories;

① AI-Cu alloy, ② AI-Cu-Si alloy, ③ AI-Si alloy, ④ AI-Mg alloy, ⑤AI-Zn-Mg alloy and ⑤ AI-Sn alloy.

Detailed explanation of welding procedures for aluminum and aluminum alloys

This procedure specifies the fundamental requirements for welding aluminum and aluminum alloys, and is applicable to the aluminum welding process of aluminum and aluminum alloy single-layer containers and aluminum-lined containers welded by manual tungsten argon arc welding, gas welding or condensation argon arc welding.

A, welding data:

1. The purity of argon for welding shall be ≥99.99%, and the dew point shall be ≤-55℃, which shall conform to the rules of GB/T4842 or GB10624. When the pressure of bottled argon is less than or equal to ≤0.5Mpa, it should not be used. (The nitrogen content in argon is ≥0.04%, otherwise light yellow or grass green magnesium nitride and pores will be produced on the weld surface; Oxygen content ≥0.03%, otherwise dense black spots, unstable arc and large splash can be found on the surface of the molten pool; When the water content is ≥0.07%, the molten pool will boil and blowholes will be generated in the weld).

2. The manual TIG welding electrode adopts cerium tungsten electrode. The electrode diameter should be selected according to the welding current (generally, the tungsten electrode with a size larger than that required by the welding current is used), and the electrode tip should be hemispherical (manufacturing hemispherical method: use the tungsten electrode with a size larger than that required by the welding current, grind the end into a cone shape, vertically clamp the electrode, strike an arc on the test plate with a current larger than that required by the used tungsten electrode for a few seconds, and the tungsten electrode tip will be hemispherical. If the tungsten electrode is polluted by aluminum, it must be re-polished or replaced; When the pollution is slight, the current can be increased to make the arc extinguish on the test plate for a while, which can burn off the pollution):

Cerium-tungsten electrode diameter mm22.53.24.05.0

Welding current A100 ~ 200170 ~ 250200 ~ 300350 ~ 480500 ~ 675 (during direct connection)

Welding current A15~2517~3020~3535~5050~70 (in reverse connection)

(AC) welding current A85 ~ 160120 ~ 210150 ~ 250240 ~ 350330 ~ 460

3. When welding aluminum alloy with MIG, because the aluminum welding wire is relatively soft, in order to prevent the welding wire from biting, the wire feeding wheel is not allowed to use the wire feeding wheel with gear, and it is not suitable to use the wire pushing type; Spring tubes are not allowed to be used for wire feeding hoses, but PTFE or nylon products, otherwise the hoses will be polluted or blocked due to grinding. MIG usually uses DC reverse polarity.

4. The main function of flux is to remove oxide film and other impurities. When it is used, it can be made into paste with anhydrous alcohol or directly put flux powder on the groove and both sides. When welding fillet welds, those fluxes that are easy to remove slag after welding should be selected; Flux for Al-Mg alloy should not contain sodium composition.

5. When welding different brands of aluminum materials, when there are no rules in the drawings and processes, the welding wire data shall be selected according to the parent material with better corrosion resistance and lower strength grade. When welding corrosion-resistant aluminum alloys such as Al-Mg alloy or Al-Mn alloy, it is advisable to use welding wires with magnesium content or manganese content close to or slightly higher than the base metal. The welding wire can be selected from GB/T10585 Aluminum and Aluminum Alloy Welding Wire, GB/T3190 Chemical Composition of Deformed Aluminum and Aluminum Alloy and GB/T3197 Aluminum and Aluminum Alloy Wire for covered electrode.

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