Quick answer: Aluminium is usually much lighter than stainless steel and is often non-magnetic, but appearance and a simple magnet test cannot prove the alloy. For purchasing, fabrication or failure analysis, combine weight, surface condition and traceable documentation, then use XRF or OES when the exact grade matters.
| Check | Aluminium | Stainless steel | Limitation |
| Weight | Density is typically about 2.7 g/cm³ | Density is typically about 7.7–8.0 g/cm³ | Compare parts of known and similar volume |
| Magnet | Normally not attracted | Austenitic grades may be weakly magnetic after cold work; ferritic and martensitic grades are magnetic | A magnet cannot identify the exact alloy |
| Surface | Often light grey; anodized or coated surfaces vary | Commonly brighter, with mill, brushed or polished finishes | Finish and contamination can mislead visual inspection |
| Spark test | Usually produces few or no grinding sparks | May produce visible sparks depending on grade | Damages the surface and is unsuitable for finished parts |
Review the purchase order, material certificate, heat number, specification and grade marking first. Documentation is more useful than appearance when material identity affects load capacity, corrosion resistance, welding or regulatory acceptance.
For parts of the same dimensions, aluminium is roughly one-third the density of stainless steel. Use magnet response only as a supporting observation because many common 300-series stainless grades are non-magnetic or only slightly magnetic.
Portable XRF can rapidly distinguish aluminium-rich material from iron-chromium-nickel stainless steel and identify many alloy families. However, XRF does not measure light elements such as carbon reliably. OES or laboratory analysis may be required when carbon content, an L-grade designation or a tightly controlled aluminium chemistry must be confirmed.
Do not rely on uncontrolled acid, bleach or chloride tests. They can stain aluminium, attack stainless steel, contaminate the surface and create a safety hazard. Grinding, filing and scratch tests also damage finished products and may invalidate acceptance requirements.
Review the available stainless steel product range when defining the required form and specification.