How To Weld Aluminum To Steel

How To Weld Aluminum To Steel - You can join aluminum to any metal using either mechanical fastening, or adhesive bonding. 

How To Weld Aluminum To Steel

To weld aluminum to steel, however, you will need to use other techniques like arc or friction welding.

These are further explained below.

Why is it necessary to weld aluminum to steel?

Aluminum and its alloys are lighter than steels. 

They have a density of 2.70 g/cm3, compared to 7.75 to 8.05 for steels. 

A comparable amount of steel will weigh three times as much as aluminum.

Steel is used in many industries for various structural purposes. 

Steel has a high density, which means that it comes with a heavy weight penalty. 

Transport industries are being forced to adhere to strict limits on greenhouse gas emission by new environmental laws. 

To reduce emissions, one way is to lower the vehicle structure's weight. 

It is important to replace various steel structures with aluminum alloys. 

It is often not possible to replace all of the steel structures with aluminum alloys. 

Therefore, it is necessary to join them.

Although aluminum alloys can be joined to other steels using methods such as brazing or mechanical fasteners, welding is recommended for those with superior structural integrity. 

It is not easy to weld aluminum alloys to stainless steel.

Why is it so difficult to join Aluminum to Steel?

The metallurgy of steel and aluminum alloys is very different. 

They have different physical properties such as thermal conductivity, melting temperature, and metallurgy. 

The melting temperature of steel is generally around 1370°C. 

This is more than twice the melting point for aluminum, which melts at around 665°C. 

Each of these metals are virtually insoluble in each other despite their differing melting points. 

They react with each other to form intermetallic phases. 

The above issues can pose challenges when fusion welding is done, as in the case of arc welding of aluminum and steel. 

Due to their fragile nature, the resulting welded joints are often not suitable for industrial applications.

How can you join Aluminum and Steel?

Fusion welding is a difficult process for joining steel to aluminum. 

This is due to dissimilar melting points, thermal conductivities and expansion coefficients, as well as the tendency to create brittle intermetallic compound. 

Fe solubility is low in Al (around 0.04wt%) and at temperatures greater than 350°C Fe diffusion into Al can become significant. 

This causes precipitation of Fe/Al intermetallic compound. 

Significant intermetallic precipitation can occur below the melting point for aluminum (660 C in pure Al). 

Diffusion is the main driver of intermetallic precipitation. 

It is affected by the temperature and time history of the interface between Fe and Al.

Lasers can be used to create brazed joints between steel and aluminum. 

The high intensity heat generated by lasers in a small area means that it is possible to quickly create a stable brazing environment and move it quickly to form a joint with minimal diffusion. 

The Fe-Al phase diagram illustrates the variety of intermetallic phases possible, including Fe3Al (892HV), FeAl (470HV), FeAl2 (1060HV), Fe2Al5 (103HV) or FeAl3 (992HV). 

These phases have a high hardness, low ductility, and poor fracture toughness. 

These phases are essential for thermally producing a joint between steel or aluminum. 

The thickness of the intermetallic compounds layer must be as thin as possible to ensure good mechanical performance. 

First, you can use an aluminum coating on the steel. 

You can do this by hot dipping the steel in molten aluminum (hot dip-aluminising). 

The aluminum can then be arc-welded to the aluminum coat. 

It is important to avoid the arc heating of the aluminum to a high temperature. 

Otherwise, there are potential hazards for intermetallic compound formation.

Another way to reduce intermetallic formation in fusion welding is with bimetallic transition inserts.

These inserts are made up of one piece aluminum and one piece steel. 

They can be bonded together by rolling, friction welding, flash welding, flash welding, or hot pressure welding.

The bimetallic joint is then individually welded on to the bulk aluminum and steel. 

The bulk aluminum should be welded first to the aluminum part of the transition joint. 

This creates a greater heat sink when bulk steel is arc-welded to the steel portion of the insert.

When joining these materials, the primary goal is to keep the temperature of the weld as low as possible and minimize the time it spends exposed to high temperatures. 

To produce bimetallic transition elements between aluminum alloys and steel bulk parts, friction welding (primarily rotary) is used.

Rotating one piece relative to the other while being subjected to a compressive force is what Rotary friction welding does. 

Heat is produced by friction between surfaces, which causes the interface material to become plasticized. 

The interface material is displace by the compressive force, which promotes metallurgical joining.

Friction welds do not enter the liquid state and remain cooler during processing. 

Friction welding is fast, so it prevents the weld from being exposed to high temperatures for long periods of time. 

Because friction welding reduces intermetallic compound formation, it is widely used in commerce to join dissimilar materials.

While friction welding has many benefits, it is still important to select the right parameters. 

An interlayer of pure aluminum is often used when welding stainless steel and steel to an alloy of aluminum. 

This drastically reduces the formation of intermetallic. 

Intermetallic compounds formed between friction-welded steels and aluminum alloys are iron-aluminum-based. 

Therefore, it is expected that brittle compounds will also form between steel and pure aluminum. 

Pure aluminum is more soft than an aluminum alloy. 

This means that pure aluminum is more malleable than an alloy of aluminum. 

Lower temperatures reduce the risk of brittle compounds.

Because it is difficult to produce strong welds between these two materials, many commercial applications of joining aluminum alloys and steel use mechanical fasteners. 

Depending on the application, galvanic corrosion must be prevented when using mechanical fasteners. Galvanic corrosion is more common in the aluminum alloy.

This can be prevented by insulating the aluminum alloy from steel. 

This is usually done using an insulating coating, or paint.

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