Steel & Aluminum Comparison Chart
The grades that come up most often on the floor, compared at a glance.
Steel
| Grade | Machinability | Relative strength | Typical use |
|---|---|---|---|
| 1018 | Excellent | Low–moderate | General purpose, shafts, brackets, non-critical parts |
| 1045 | Good | Moderate | Shafts, gears, parts needing more strength than 1018 |
| 4140 | Fair | High (especially heat treated) | High-stress shafts, tooling, structural components |
| 303 stainless | Good (free-machining) | Moderate | General stainless parts, fittings, fasteners |
| 316 stainless | Poor (gummy, work-hardens) | Moderate | Food, medical, marine — where corrosion resistance matters most |
Aluminum
| Grade | Machinability | Relative strength | Typical use |
|---|---|---|---|
| 6061-T6 | Excellent | Moderate | General purpose, weldable, most common aluminum grade in a shop |
| 7075-T6 | Good | Very high | Aerospace and high-stress parts; not weldable |
| 2024-T3 | Good | High, good fatigue resistance | Aircraft structure and skins |
| 5052 | Good | Low–moderate | Sheet metal, tanks, marine parts — good corrosion resistance |
Machinability isn't just about hardness
A gummy, work-hardening material like 316 stainless can be genuinely harder to get a good finish on than a much harder but more brittle material, because it tends to smear and build up on the cutting edge rather than shearing cleanly — machinability describes how the material actually behaves under a cutting edge, which doesn't always track directly with strength or hardness numbers on a spec sheet.
Why 7075 and 2024 aren't weldable, and it matters
The same heat treatment that gives 7075 and 2024 their high strength gets undone by the heat of welding, leaving a weakened zone right where the weld was — these grades are chosen specifically for machined or mechanically fastened structure, not for anything that needs a welded joint. 6061 welds reasonably well by comparison, which is part of why it's the default choice when a design needs both machined features and welded assembly.
This is a starting point for material selection, not a substitute for a spec
Actual mechanical properties vary by exact temper, bar stock vs. plate vs. cast, and specific supplier certification — when a print or engineering requirement calls out a specific grade and temper, pull the actual material certification rather than relying on general comparisons like this one.