Aluminum and Its Alloys
Although aluminum is lightweight and low-strength metal, some aluminum alloys are becomes four times stronger than mild steel after alloying some ingredients.
Characteristics of Aluminum and Its Alloys
Aluminum possesses the following characteristics:-
- It is a silvery-white metal.
- It is a light metal, with a density of about a third that of steel or brass.
- It is a good conductor of electricity.
- It is a good conductor of heat.
- Aluminum is a non-magnetic, malleable, and ductile metal.
- The Melting point of pure aluminum is about 659ºC.
- The fusion range of most aluminum alloys is between 520ºC to 650ºC.
Aluminum and Its Alloys are currently being used more than pure aluminum because pure aluminum is not particularly strong, It combines with other metals such as Copper(Cu), chromium(Cr), nickel(Ni), iron(Fe), zinc(Zn), manganese(Mn), silicon(Si), and magnesium(Mg), etc, to form high-strength alloys.
Aluminum and Its Alloys may be:-
- Rolled, etc.
Welding characteristics of Aluminum and Its Alloys
Welding aluminum and its alloys is a challenging task as compared to other metals because aluminum has certain welding characteristics which require some special attention during welding. like:
A thin film of oxide is always present on the surface of the aluminum which contains moisture that may react during fusion welding, which can cause of formation of oxidation and liberate hydrogen which can cause porosity.
In the case of aluminum alloys, on solids, both strength and ductility are low, so the metal is prone to cracking when welded under restraint.
Removing oxides :
- The oxide film on the surface of the base metal has to be removed before and during welding. Chemical or mechanical brushing, scrubbing, etc are used to remove oxides.
- A suitable flux material is used in gas welding and brazing of aluminum and its alloy.
- For stick welding, suitable thickly coated electrodes are used.
- DCRP (electrode +) has been found to be effective for MIG welding whereas AC is used for tig welding of aluminum.
As we know, aluminum being a very good conductor of the heat dissipates heat from the joint to the adjacent base metal being welded,
The following measures are taken to compensate for the heat loss due to the joint being welded:
- The size of the nozzle used for aluminum welding is comparatively larger than normalgas welding of steel. Similarly, the welding current is also kept slightly higher than steel welding.
- The thick section of base metal is preheated before welding.
- Welding heat can cause distortion and buckling, proper joint design and edge preparation will counteract this tendency.
- It can be difficult to determine when a metal begins to melt or when the proper welding temperature has been reached. because aluminum does not show any color when heated. However, a sign of heating is that the dry flux begins to melt and blister on the surface of the metal, indicating that an appropriate welding temperature has been achieved.
- Due to its high thermal conductivity and low melting temperature, aluminum alloys conduct heat faster than normal steel. The preheat limit for this should be 400ºF (204ºC)
Although welding aluminum requires more skill than other metals, it can be accomplished by a number of welding processes with some special attention and pretreatment.
The methods employed for welding aluminum and its alloys can be described as follows:-
Types of Welding Aluminum
- Oxy-Gas Welding.
- MIG Welding.
- Resistance Welding.
- Carbon-arc Welding.
- Metallic Arc Welding.
- TIG Weldİng.
- Solid-State Welding.
- Atomic-hydrogen welding
Oxy-Gas Welding for Aluminum
The oxy-acetylene process is quite suitable for wrought and cast aluminum and aluminum alloys. Flux is an essential component for successful welding in the oxy-acetylene process.
The oxide film (melting point of about 1930C) which is present on the aluminum surface is attacked and dissolved by flux
The flux should have some important properties like:
- Flux prevents oxidation during welding,
- A flux Must be melted at a lower temperature than the base metal so that it dissolves surface oxides before the metal can melt.
- The flux must be lighter when melted than aluminum so that it can float on any impurities on the surface, where they can be easily removed.
How to Apply Flux
Flux can be applied by several methods, such as
By dipping the hot end of the filler rod into the flux
In this method, the hot end of the filler rod is dipped into the flux and applied to the hot surface of the joint, coated flux melts from the welding heat, moves down, and flows along with the torch flame, causing it to remove oxides and cleans metal.
Brushing the flux paste on the prepared edges of the sheet
In this method, flux paste is applied with a brush to the prepared edges of the sheet before welding and after welding the adhesive flux marks should be removed from the job as a flux has a corrosive action.
Washing the job in hot water and vigorous scrubbing with a wire brush is effective to remove the flux. or It is even better to immerse in a hot solution of 5% HN03, followed by
Wash off once with warm water.
Use of fillers
If the aluminum sheet is thin then it does not require additional filler materials, additional filler materials are used only when welding thick metals
When using additional filler materials, care should be taken to ensure that it is of the same general structure as the base so that it can resist corrosion satisfactorily.
A filler rod with 5% to less than 10% silicon is often preferred for welding aluminum. such as:-
- For welding aluminum alloys, especially for heat-treated, the copper-containing type, a filler rod of 5% silicon alloy is often preferred,
There are some essential steps to be kept in mind before welding through any process like proper joint design and edge preparation
- For aluminum welding, no preparation is required other than cleaning for edges up to 2.4 mm, for sheets and tubes.
- Flange edges are not recommended in gas welding as there is a risk of flux being interpreted and the weld section may have poor mechanical strength.
- If the thickness of the material is 2.4 to 6.4 mm then the edges of the material should be beveled
Metallic Arc Welding
Aluminum can be welded by Metallic Arc Welding or stick welding process. The unstable arcs between aluminum electrodes and base metals complicate this process.
Even Thought Aluminum Welding Has Some Complexity to the Stick Welding Process, Selecting the Right Kind of Electrode and Welding Setup with a Fair Amount of Experience, Can Minimize these Complications.
Some special things have to be noted before welding aluminum by the stick welding process, such as
- Surface Preparation,
- Surface Cleaning,
- Power supply,
- Selection of electrodes,
- Preheating of Job, and
- proper Welding Technique.
Aluminum sheets up to 6 mm can be welded by making a butt joint with a simple gap, but it would be appropriate to weld more than this by making a sheet of more thickness.
How to prepare
Fix the selected parts for aluminum welding with the help of clamps or fixtures. If required, plan a backing strip, it is preferred by made of copper or steel.
A backing strip makes a joint, small convex that prevents melted aluminum from flowing through joint faces.
The gap between aluminum plates to be welded may either be Vee-shaped or parallel. The taper may be of the order of 1.6 mm at
the beginning and increase at a rate of 1.6 mm/300 mm run of
weld along the length of the seam.
A parallel gap width ranges from 1.6 mm to 3.2 mm or about half the thickness of the metal welded in order to allow the arc to melt both edges simultaneously.
Cleaning the Surface of Aluminium and its alloys
The surface of the aluminum and its alloys should be thoroughly cleaned of all types of debris, dirt, oil, grasses, oxide, etc. it should be cleaned mechanically or chemically.
Due to a good conductor of heat, aluminum, and its alloys require more heat that can be obtained by a short arc length and DCRP current (20 volts).
Welding electrodes of aluminum and its alloys
The most frequently used aluminum electrodes are heavily coated electrodes of 5% Si-Al alloy, These electrodes are coated with a special flux that is very sensitive to moisture.
Some aluminum electrodes (a core wire of 99.5% aluminum) are used for welding vessels of pure aluminum as used in food and chemical industries, where corrosion must be prevented.
Preheating of Job
As previously discussed, the appearance of moisture on the surface of “aluminum and its alloys” can cause porosity and crack.. To prevent these types of defects, preheating approx 200-degree centigrade is required before starting welding aluminum.
The most important step in aluminum welding is the welding technique as aluminum welding requires comparatively more skill. these steps can be discussed as follows:-
- The arc is produced between the electrode and the job,by the scratching method.
- Compared to other processes, aluminum welding requires a slightly higher scratching force, due to the heavy coating and surface oxides.
- After the arc is generated, the electrode is placed at right angles and the electrode coating almost touches the molten pool. Weaving is not done.
- The purpose of holding the electrode at right angles is to direct the arc so that both sides of the joint are properly and evenly heated.
- Arc welding aluminum is about three times faster than welding steel. The welding should be started at a uniform rate and the welding speed should increase as the metal heats up.
factor affecting steps of Aluminum welding
- The joint surface should prepare if required.
- The surface of metal should be cleaned thoroughly either mechanically or chemically.
- Slag must be removed from each bead
- The speed of welding must be increased when the workpiece is heated.
|Plate thickness||Electrode diameter mm||Edge preparation Gap||Current Amp|
|95||5.9||4.8 mm orbeveled 700 with1.6 mm gap||200-225|
- Since the flux/slag is very corrosive, the weld must be washed and brushed with hot water or(5% solution of HN03 in water ) after it has cooled down.
Production and use of Aluminum and Its Alloys
There is an intense demand for (Al )and its alloys in the market today. This demand has mainly arisen due to their attractive design along with their physical, mechanical, and chemical properties.
According to a report by The International Aluminum Institute (IAI), the production of primary aluminum in 2022 is about 5,805 thousand metric tonnes. while total production of aluminum for May 2022 is 11,728 thousand metric tonnes.
This reveals about the future of aluminum in the coming times, that it will prove to be a better option due to its light weight and strength.Source: IAI
Al and alloys are frequently used in the following fields:
It is widely used in the transportation sector, such as in the manufacture of modern vehicle structural components, engine parts, trim and decorative features, hardware, doors, window frames, tanks, furnishings, fittings, and many other components made of aluminum alloys are used in trains, trucks, buses, automobiles, cars, and airplanes, etc.
The consumption rate of aluminum alloys is also high, in the food sector, aluminum alloys are used for the manufacturing of food preparation equipment, refrigeration, storage containers, bakery equipment, shipping containers, etc.
Aluminum and its alloys are often used in process industries to manufacture tanks, drums, pipes, heat exchangers, gratings, smokestacks, Drilling Towers, Precipitators, Centrifuges, Valves, Fittings, etc.
In Architectural fields, Al alloys are used widely to make window frames, door hardware, roofing, coping, sills, railings, fasteners, lighting fixtures, solar shading, grills, gratings, etc.
In addition, alloys and alloys are used in the manufacture of overhead conductors and heat exchanger parts, cryogenic applications, and heavy-duty structures such as dragline booms, traveling cranes, hoists, conveyors supports, bridges, etc.