The Ultimate Automobile Metal Guide

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Pistons, side panels, frames, exhaust pipes: Automobiles are a stunning amalgamation of so many different parts. And with so many parts comes many different types of metal: Aluminum, cast iron, and stainless—just to name a few. Any skilled welder knows that every type of metal is unique. Each has its own weaknesses, strengths and secrets for welding the right way. In this guide, we’ll cover some of the best tips for welding the most common metals found in automobiles.

The Breakdown

Before we jump into each type of metal, it’s important to understand the basic breakdown of your average vehicle. This, of course, truly depends on the type of automobile and when it was built. That being said, we can get a general idea by looking at a graph of the modern automobile.

breakdown of what's in a car

You’ll notice that steel makes up a significant chunk of the automobile’s total material. For newer vehicles, aluminum has begun replacing steel, meaning this number might be higher or lower depending on the year your vehicle was manufactured. Older automobiles also tend to have a higher amount of cast iron parts, although even modern vehicles contain about 8%.

Overall, steel, aluminum and cast iron are usually the main metals used in automobiles. However, there are some performance vehicles that use other types of material such as chromoly, which helps reduce the weight of the automobile or motorcycle.


Every year, more and more vehicles are replacing steel parts with aluminum. Within the trailer industry, some companies are ditching steel altogether for aluminum. The two big reasons are that: 1) Aluminum is lighter than steel. 2) Aluminum doesn’t rust.

TIG welding

Ultimately, the battle between aluminum and steel is a tricky one, especially for welders. Many welders prefer mild steel, simply because aluminum can be very tricky to weld. Because of its material properties, MIG or stick welding aluminum is incredibly difficult to do well. Often you’ll get horrible warpage or welds that just don’t stay together. Most experts suggest AC TIG welding aluminum with a foot pedal. The foot pedal allows you to vary the amperage as you weld, making it easier to keep your heat low, preventing warpage or burn through.

If you need to TIG weld aluminum and have been looking for a multiprocess machine, make sure you go with either the ESAB Rebel 205ic or the Miller Multimatic 220. They’re the only two multiprocess machines on the market that can AC TIG weld.


Plate metal makes up about 2/3rds of the steel used in most vehicles. While you can weld steel plates using any process, the trick is to manage your heat. If you go in with the trigger held down like Rambo, your plates are going to warp and you might even burn through the thin material. For repairing car panels, check out our in-depth guide. The best strategy is generally to weld in quick bursts and allow the panel to cool down between welds.

Welding mild steel

Besides the body panels, most car frames are also made up of tough mild steel. While the metal used here isn’t particularly tricky, you’ll want to make sure you’re getting good welds with strong penetration. The frame is literally the backbone of your vehicle. If you're new to welding, it’s recommended you stay away from messing with it. The last thing you want is your vehicle splitting in half while you’re out on the road.

Stainless steel is also used in vehicles, though often not nearly as much. Remember to purge and manage your heat with stainless to help the material keep its stainless properties.

Cast Iron

Vintage cars tend to have more cast iron parts, though even modern vehicles have a moderate amount of the material in them. The reason for this is that cast iron is incredibly good at dealing with heat. As we mentioned above with aluminum or even steel plates, both materials can warp or distort under heat. Cast iron, on the other hand, takes high temperatures like a champ. This is why so many engine parts are still made from cast iron.

Engine block

For anyone who has welded cast iron correctly, you’ll know it’s not always easy. However, it is definitely possible. Most cast iron parts are gray cast iron. When welding this type of material, it’s important to avoid drastic temperature changes. For this reason, most welders will prefer to pre-heat before welding and allow ample time for cooling.

Even when done correctly, oftentimes you'll find small cracks near your welds with cast iron. If your weld needs to be watertight, you’ll probably want to apply some sort of sealing compound.

Other materials

Besides these 3 materials, vehicles can also have copper and other types of metal used in them. For high-end vehicles, chromoly is often used to replace steel or aluminum. For more information on chromoly, check out our in-depth post here.

Which Machine Is Best for These Materials?

Automobiles aren’t your typical welding project. They’re not an iron fence or a steel cart, where you’re only dealing with one type of metal. Because of this, suggesting a single machine can be difficult.

Ultimately, it depends on what you plan to do. If you’re looking to build heavy, durable parts for your offroad vehicle, you can easily get away with a solid MIG machine. But if you work on every part of your vehicle, you really should consider one of the new multiprocess machines. The fact that they can now TIG weld aluminum is a massive gamechanger, and the cost is quite reasonable when you realize you’re truly getting 3 machines in one. Check out the Miller Multimatic 220 and ESAB Rebel 205ic for more details.

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