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Most Cast Aluminium can be welded. Some tend to be a little bit tough or just plain out impossible to weld. The 3xx.0 families (356.0, 357.0, and 319.0) are treatable by heat and can be welded with the aluminum filler alloy 4043. The 3xx.0 family are Aluminium-Silicon-Magnesium alloys except for 319.0 cast aluminum, which contains copper. The Al-Mg 5xx.o alloys like the 535.0 are also readily weldable with the 5356 filler, and they are also not heat-treatable.
Factors That Determine The Weldability Of An Aluminium Casting.
Two important factors determine the weldability of aluminum casting.
1. The Casting’s Composition
As stated earlier, the 7xx.0 AlZn families can be difficult to weld. They are also treatable by heat treatment, and they can be welded using 5356 Aluminium filler. Some of the 7xx.0 series cannot be welded. The 3xx.0 series, including 356.0, 357.0, and 319.0 aluminum casting, are treatable by heat and can also be welded as base materials with aluminum filler alloy 4043.
2. The Manufacturing Process (How It Was Made)
There are at least four different processes which include:
- Investment casting
- Permanent mold casting
- Sand casting
- Die casting
It’s entirely possible to weld investment castings, permanent mold castings, and sand castings. This is possible because the molten aluminum is cast into a mold that is poor in conducting heat. So the casting takes a while to solidify, allowing dissolved gases in the molten aluminum to escape.
For die casting, the molten aluminum is injected with pressure into a water-cooled steel mold, making the molten aluminum solidify rapidly. The process prevents any gases from escaping, resulting in gas pockets in the casting. This can only be corrected by grinding out the pocket and repairing- welding it. The die casting can also be welded, only that it requires more care and caution from the welder than investment, sand, and permanent mold casting.
Die Castings: How To Identify Them
- It has a smoother surface finishing than investment, sand, and permanent mold casting.
- You will find noticeable ejector pin marks on both the inside and the outside of the casting. These marks are about one-eighth inches, measuring in diameter.
How To Prepare Cast Aluminium For Welding
- You can use mild alkali or a solvent to clean up oil, grease, or water vapor.
- Use a wire brush, a strong base solution, or an acid to remove surface oxide.
- Put the joints together by arranging them appropriately.
- Ensure the joints are dry and keep them that way.
- Weld in a few days.
Difficulties Of Welding Cast Aluminium
Aluminum requires extra care and caution during welding due to its peculiar properties, such as its susceptibility to impurities in its molten state, making it porous and weak. Other peculiarities include its softness, sensitivity, and the toughness of the oxidized layer it is insulated with.
Aluminum melts at 1200°F (650°C), and its protective oxide melts at a higher temperature of 3700°F (2037°C), and because of this, you must clean off the oxide properly to make welding possible. Aluminum can easily be contaminated by dirt, air, water, and even hydrogen, which can hinder a perfect welding job.
Another difficulty you may encounter while welding aluminum is a variation in the thickness of different materials. So the operator has to be extra careful not to ruin thinner matter while welding thick materials.
Types Of Aluminum Welding
Choosing the proper welding process is very important when it comes to aluminum due to its many peculiarities.
You must also be sure to put on a proper outfit or gear while welding. Dawning the right set of protective armor while welding would help keep you safe from any dangers that could accompany the job. Protective gears like shaded glasses, a welding helmet, and appropriate boots. You should also not forget to have a fume ventilator right next to you.
Let’s now take a look at the two most common types of welding.
GTAW/ TIG Welding
Gas Tungsten Arc Welding or Tungsten Inert Gas welding needs constant current equipment with AC (alternating current) capability. This process uses 100% argon as a protective gas, and it doesn’t require a mechanical wire feeding. Instead, it feeds the filler material into the puddle. This process is considered clean because the alternating current acts as a cleaner, removing the oxidized layer that protects the aluminum as you weld. It keeps the aluminum untarnished throughout the welding process. Tig welding aluminum is often the preferred method.
TIG Welding Tips
- Pick out the right tungsten rod
- Cleaning and preheating the aluminum is an important step you shouldn’t forget.
- Monitor the argon flow to prevent the torch from getting too much of it. This can lead to you having an irregular arc.
- Use a heat sink
- Melt the filler rod to create a welding pool.
GMAW/ MIG Welding
Gas Metal Arc welding/ Metal Inert Gas Welding. This process has a higher deposition rate than Tungsten Inert Gas welding, which affects the quality of the weld. It moves fast, and it needs a mechanical feeding system with a spool gun or push-pull gun for feeding to happen.
Moisture is not a friend when it comes to this process. You must ensure to keep the base material and aluminum rod from moisture to prevent porosity.
MIG Welding Tips
- Ensure that your push-pull feeding wire is set and ready to work.
- Clean the aluminum and file the edges you want to join together
- You should push at a 10°- 15° angle
- To avoid defects and improve the overall appearance of the weld, use a multiple pass straight bead.
- Ensure heat sinks are used. By using heat sinks, you can weld at a slower pace and avoid defects.
Other Types Of Aluminum Alloy Welding
Laser Beam and Electron Beam Welding
This technique is known commonly as a welding technique. Aluminum is a sensitive material and calls for cautious techniques when it comes to welding. The electron beam welding can be controlled with ease, and it is perfect for aluminum that can be easily damaged. On the other hand, the laser beam welding technique is ideal if you are looking for fast, clean welds. Taking into consideration the nature of aluminum that is also susceptible to cracking. This technique easily evades that complication.
By contrast, this form of welding involves passing an electrical current through the parts that are to be joined together while applying pressure. However, this requires knowledge of the metal’s thermal and electrical conductivity.
Shielded Metal Arc Welding (SMAW)
The welders least like this method when it comes to welding. It is used to repair aluminum cast using a constant current machine with an aluminum electrode using electrode positive polarity.
Can Cast Aluminum Be Fixed?
Cast aluminum is used in various equipment and machines comprising cars, and any form of motors, pipes, vents, and various housing features. Aluminum is resistant to corrosion. It is a soft type of metal, meaning it can be easily punctured or cracked.
Can aluminum be fixed? Yes, aluminum can be fixed. To fix these flaws in cast aluminum, you can use a torch and an aluminum brazing rod. Aluminum brazing rods are a combination of aluminum and zinc. These aluminum brazing rods melt at a lower temperature than pure aluminum. This makes melting the rod easy and filling it into the cast aluminum to patch the cast aluminum parts. This should be done with vare, considering the softness of the aluminum.
Most aluminum castings can be welded, so the short answer is yes. However, when it comes to casting weldability, there are two factors to consider: Its composition and how it was manufactured. Once you know these two points, you can figure out whether it is weldable or not.
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