Steel and iron castings are roughly three times the density of aluminum, but aluminum has a lower elastic modulus, so a 1:1 section usually has to become deeper or differently ribbed to match bending stiffness. As a published example, a trailer connector squeeze cast in A356.2-T6 and redesigned from a steel casting reported at least 54% weight reduction (company-reported); that is an outcome of one project, not a forecast for your part.
Key points
- Steel and iron castings are roughly three times the density of aluminum, which is why moving trailer parts are reviewed for aluminum.
- Steel to aluminum is a design change, not a material swap; a 1:1 section will not behave the same way.
- Aluminum has a lower elastic modulus, so sections usually become deeper or differently ribbed, and bending stiffness is checked on the new section.
- Keep steel or iron where stiffness, wear, impact or thermal duty dominate, or where the surrounding structure and fasteners cannot change.
- Squeeze casting fills at low velocity and solidifies under pressure, so an A356-T6 part can be heat treated and welded, which a conventional die casting usually cannot.
- Fasteners, interfaces, fatigue, corrosion and thermal expansion must be re-checked for the aluminum design.
- Published trailer examples are original project outcomes, not a forecast for another part.
- The business case compares finished part with finished part, not casting price with casting price.
Steel vs aluminum comparison: what changes on the part
Use this as a review checklist, not as a material substitution rule. The aluminum column refers to A356-T6 squeeze casting; the steel or iron column is the existing route that must be re-checked.
| Factor | Steel or iron casting | Aluminum squeeze casting (A356-T6) |
|---|---|---|
| Density and weight | Roughly three times the density of aluminum. | A356 density is 2.68 g/cm³, used for weight estimates, not acceptance. |
| Stiffness and section design | Stiffness is one reason to keep steel; a 1:1 aluminum section will not behave the same way. | Lower elastic modulus; sections usually get deeper or differently ribbed; check bending stiffness of the new section. |
| Strength reference | The existing steel route is the baseline; compare the finished part against the original function. | A356-T6 reference values: 260–320 MPa tensile and 220–260 MPa yield (company-reported); for first feasibility, not acceptance. |
| Welding and T6 | The existing route is the baseline for the finished-part comparison. | Squeeze casting can be T6 heat treated and welded; the heat-affected zone loses T6 strength. |
| Corrosion and contact with steel | Corrosion and duty cycle are re-checked for the aluminum design. | A356 holds copper to 0.2% or less, which keeps corrosion behavior good when bolted to a dissimilar metal; galvanic isolation still needs review. |
| Fasteners and interfaces | Bolt bearing and thread engagement change with the parent material. | Bolt bearing, thread engagement and galvanic isolation change with the parent material; interfaces must be reviewed. |
| Where it usually stays the better choice | Where stiffness, wear, impact or thermal duty dominate, or where structure and fasteners cannot change. | Evaluated when weight matters and sections and fasteners can be redesigned. |
Where the weight saving comes from — and why a 1:1 swap fails
Steel and iron castings bring stiffness, wear resistance and predictable cost, at roughly three times the density of aluminum. Where the part moves, its weight becomes a cost in payload, fuel, handling and in the loads the surrounding structure has to carry.
But steel to aluminum is a design change, not a material swap. A 1:1 steel section in aluminum will not behave the same way: sections usually get deeper or differently ribbed to match bending stiffness. Aluminum has a lower elastic modulus, so bending stiffness of the new section has to be checked rather than inferred from the old drawing.
The weight that comes out is the result of that redesign, not a conversion factor. Thinner walls are possible when pressure controls solidification, and that is where weight and cost come out. A conversion review compares finished part against finished part: tooling, machining, heat treatment, inspection and scrap on the same quantity. Casting price against casting price is not a conversion case. The steel-to-aluminum conversion review is the place to test whether the section, fasteners and validation can support the change.
When to keep steel
Keep the steel or iron casting where stiffness, wear, impact or thermal duty dominate. Also keep it where the surrounding structure and fasteners cannot change, because the aluminum design cannot be treated as a drop-in.
Sand or gravity casting is usually the better choice for prototypes, low volume, and large simple parts with modest mechanical needs. Squeeze casting is evaluated when shrinkage rejects or excess section weight are the reasons the part is being reviewed. If the existing route is the better answer, the buyer should get a documented reason, not a quotation. The gravity and low-pressure conversion comparison is useful when the question is process route rather than material.
Published trailer examples
The examples below are company-reported outcomes from the original projects. They show what was reported, not what another part will achieve.
| Part | Change | Reported outcome |
|---|---|---|
| Trailer connector | Steel casting replaced by A356.2-T6 squeeze casting; redesign. | At least 54% weight reduction reported (company-reported). |
| Trailer beam | Steel replaced by A356.2-T6; produced as one casting. | Substantial weight reduction reported, no figure published (company-reported). |
| Trailer bracket | Sand casting replaced by A356.2-T6 squeeze casting; weldable. | About 50% higher strength and markedly higher production efficiency reported (company-reported). |
Published outcomes are the results of the original projects, not a forecast for another part. The business case is built from the buyer's own drawing, volume and validation requirements.
What has to be re-validated on the aluminum design
The review should cover stiffness, not only strength. Check bending stiffness of the new section, then check fasteners and interfaces: bolt bearing, thread engagement and galvanic isolation change with the parent material. Re-check fatigue and service duty, including temperature and corrosion, for the aluminum design. Validate the finished part with tests against the original function.
If the part mates with steel, state thermal expansion on the drawing; A356 thermal expansion is 21.4×10⁻⁶/°C. Show weld locations on the drawing, because the heat-affected zone loses T6 strength. State properties by section where a load path matters, with specimen locations. Welding is not listed in CEX's published in-house scope; weld procedure and welding responsibility are agreed per project. See the welding of squeeze-cast aluminum parts for the questions to settle before quoting.
For mechanical property callouts, use the guide to specifying mechanical properties in castings so the specimen location and test method are not left open.
What to put on the drawing and RFQ
Send a package that lets the foundry review the part as a finished component, not as a material swap. The structural casting RFQ requirements set the expected level of detail for beams and arms.
- Drawing and model with revision, material specification and condition.
- Alloy named exactly: A356 or A356.2, with the governing standard and T6 condition; A356.2 has a tighter composition window, and the two are not interchangeable without checking the drawing.
- Load case and stiffness target, including where bending stiffness has to be met.
- Weld locations and properties by section, with specimen locations where a load path matters.
- Mating steel parts, fastener details and galvanic isolation requirements; state thermal expansion if the part mates with steel.
- X-ray zones and the drawing note: "MATERIAL A356.2 to [standard], T6; MECHANICAL minimums on specimens from zone ___; SOUNDNESS X-ray of zones ___; No repair welding or impregnation without written approval."
- Initial and annual quantities, plus the target sample date.
- Submission level and customer-specific requirements.
- Mandatory acceptance criteria separated from preferences.
- Finished-part cost basis: tooling, machining, heat treatment, inspection and scrap on the same quantity.
Name the alloy and standard on the drawing rather than leaving "aluminum" as the specification. The A356-T6 squeeze casting specification page is the reference for the alloy and condition.
What CEX can and cannot confirm
CEX can review the squeeze casting window: presses from 300 to 1,100 t, wall thickness from 4 to 15 mm, part envelope up to 1.2 × 0.8 m, and as-cast blank tolerance of ±0.2 mm, with machined tolerances agreed per feature (company-reported). These limits are not all reachable on one geometry at once; they are confirmed per part at drawing review.
CEX makes die casting and squeeze casting tooling in-house, performs T6 heat treatment in-house, runs CNC machining in-house, and has X-ray and helium leak testing equipment. CEX has developed its squeeze casting process in-house since 2015 (company-reported). Production goes mainly to North America and Europe (company-reported). The inspection and leak testing capabilities are part of the review package.
CEX's IATF 16949:2016 certificate 0494978 covers manufacturing of aluminium alloy die-cast parts, with clause 8.3 product design excluded; it is valid until 2027-01-07. Design authority stays with the customer. Because design authority stays with the customer, design approval and drawing changes remain with the buyer, and the validation sign-offs are agreed per project. CEX can review and manufacture to the agreed drawing, but it does not take design authority.
Welding is not listed in CEX's published in-house scope; weld procedure and welding responsibility are agreed per project. A documented "no" is a possible outcome if the existing route is the better answer. The squeeze vs die casting selection worksheet can help frame that early review.