Choosing between aluminum vs steel parts is one of the first material decisions on a new design. Aluminum alloys such as 6061 and 7075 weigh about one third as much as steel, machine quickly and resist corrosion well. Steels such as 1018, 1045, 4140 and 4340 are about three times stiffer, much harder when heat treated, and far better in wear and high-temperature service. The right choice depends on what drives the design: weight, stiffness, wear, strength or cost.
Aluminum vs Steel: Comparison Table
Values are typical for 6061-T6 and 4140 pre-hardened. Cost is a relative per-part index including material, where one aluminum part at quantity 1 equals 100.
| Factor | Aluminum (6061-T6) | Alloy steel (4140 / 4140 PH) |
|---|---|---|
| Relative cost, qty 1 | 100 | 115 to 140 |
| Relative cost, qty 10 | 40 | 50 to 60 |
| Relative cost, qty 100 | 18 | 25 to 32 |
| Relative cost, qty 1,000 | 10 | 15 to 20 |
| Density | About 0.098 lb/in³ | About 0.284 lb/in³ |
| Stiffness (modulus) | About 10 Msi | About 29 to 30 Msi |
| Tensile strength | About 45 ksi | About 95 ksi annealed to 150+ ksi heat treated |
| Hardness | About 95 Brinell | About 28 to 32 HRC pre-hardened; higher if heat treated |
| Typical machined tolerance | ±0.001 to ±0.005 in | ±0.0005 to ±0.003 in |
| Surface finish | Ra 32 to 63 µin | Ra 16 to 63 µin; grinding for finer |
| Corrosion resistance | Good; anodizing improves it | Poor without coating; needs oxide, plating or paint |
| Lead time | Fast cycle times; widely stocked | Slower cycles; heat treat adds time if required |
| Typical use case | Housings, brackets, fixtures, lightweight structures | Shafts, gears, pins, wear parts, high-load components |
When Aluminum Wins
- Weight matters. Moving parts, handheld equipment and aerospace components benefit from lower mass.
- Machining cost. Aluminum is cut at high speeds, so cycle times are often a fraction of steel.
- Corrosion without heavy coatings. Aluminum forms a protective oxide, and anodizing adds color and wear resistance.
- Heat transfer and conductivity. Aluminum is a much better thermal and electrical conductor.
When Steel Wins
- Stiffness. For the same geometry, a steel part deflects about one third as much as aluminum.
- Wear and contact stress. Shafts, gears, pins and cams need the hardness only steel provides, often after heat treatment.
- High temperature. Aluminum loses strength quickly above about 300°F. Steel holds up much better.
- Threads in service. Steel threads tolerate repeated assembly. Aluminum threads often need inserts.
- Fatigue. Steel has an endurance limit, which makes it predictable under cyclic loads.
Common Mistakes
- Swapping steel for aluminum on a stiffness-limited part without increasing section size. The part will deflect about three times as much.
- Using aluminum for sliding or rotating contact without a hard coat or bushing.
- Pairing aluminum and steel in wet environments without isolation, which leads to galvanic corrosion.
- Specifying heat-treated steel when pre-hardened 4140 would meet the requirement and avoid an outside heat treat step.
How This Applies at Wexmar
Wexmar machines aluminum, carbon steels, alloy steels, stainless and specialty alloys every day. Our lathes, horizontal machining centers and Swiss-type machines handle both materials, and our centerless and surface grinders support fine finishes on hardened steel parts. Heat treatment, anodizing and plating are performed by qualified outside processors that we manage. See materials, parts we make, and the guides on 6061 vs 7075 and titanium vs stainless.
Getting a Quote
If you want pricing in both materials, list both on the RFQ. You can upload a drawing for an instant estimate, reviewed by a human estimator, or call (315) 400-2654.