Mild steel, stainless steel or aluminium: how to choose

Start with what the part must do

The best material is the cheapest one that does the job for long enough. Before choosing, think about strength, weight, rust, heat, appearance, and how the part will be made.

The three common choices

• Mild steel: strong, cheap and easy to cut, weld and machine. It rusts, so it usually needs paint, plating or another coating. Best for structures, frames, brackets and general parts.
• Stainless steel: resists rust and staining and looks good, and 304 and 316 are common grades, with 316 better in salty or chemical conditions. It costs more, is harder to machine and needs more care in welding. Best for food, medical and outdoor or wet use.
• Aluminium: about a third of the weight of steel, does not rust like steel, and machines easily. It is less strong than steel for the same size and needs the right alloy for welding. Best where weight matters, and for castings and enclosures.

Things people forget

• Grade matters as much as the family. Say the grade, or at least the standard, and ask for the material certificate if the part is critical.
• Availability affects delivery. A common size in stock is faster and cheaper than a rare one.
• The finish and the process can change the choice. A part that will be painted anyway may not need stainless steel.

If you are unsure

Describe where the part is used and what it must withstand. A workshop that makes such parts every week can usually suggest an option, and their advice costs nothing when you post your requirement.

Kinds of work

• Die making
• Mold making
• CNC machining
• Casting
• Fabrication