Welding Squeeze-Cast Aluminum Parts: Drawing and RFQ Guide

Key points

• Squeeze-cast parts can be T6 heat treated and welded; the low-velocity fill traps little gas, which is what makes welding practical.
• Conventional high-pressure die casting entraps gas during filling, and that porosity limits T6 heat treatment, welding and pressure tightness.
• Welding puts heat into T6 metal, and the heat-affected zone (HAZ) loses T6 strength.
• Show weld locations on the drawing and state properties by section with specimen locations where a load path matters.
• Plan finish machining of bores and sealing faces after T6, and use symmetric sections and ribs to manage distortion during quenching.
• Name the alloy and its governing standard: A356 and A356.2 are not interchangeable without checking the drawing.
• Carry the drawing note "No repair welding or impregnation without written approval."
• Welding is not listed in CEX's published in-house scope, so the weld procedure and the welding responsibility have to be agreed per project; as the buyer, state both in your RFQ.

Conventional HPDC vs squeeze casting for a welded part

For a part that will be welded, the process decision turns first on trapped gas; the alloy and the weld procedure still have to be agreed. The squeeze casting vs die casting selection worksheet sets out the same comparison as a checklist; the table below is the welded-part version, kept qualitative where no published value applies.

Why gas porosity decides weldability

Fusion welding adds heat and, usually, molten filler metal to a casting that already contains whatever gas was trapped when it solidified. In a gas-bearing casting that gas is the limiting factor: it can expand and migrate into the weld and the surrounding metal, so the joint becomes difficult to qualify and pressure tightness becomes difficult to hold. This is the practical reason a conventional die casting usually cannot be welded or T6 heat treated, and it is why gas entrapment during filling limits welding, T6 heat treatment and pressure tightness as one package rather than three separate problems.

Squeeze casting changes the filling and solidification condition rather than the alloy metallurgy. The metal enters the die at low velocity and is held under pressure while it solidifies, so little gas is trapped and thicker sections become an advantage rather than a porosity risk. That is why alloys such as A356 can be squeeze cast, T6 heat treated and welded. It is worth being precise about the claim: no casting process carries a blanket defect-free or zero-porosity guarantee, so what matters is agreeing the regions to inspect, the test sensitivity, the discontinuity limits and any leak-rate requirement for the actual part. The mechanism behind die-casting porosity is described in reviewing a porous HPDC part for squeeze casting.

What happens to T6 strength at the weld

T6 means solution treatment, quenching and artificial aging, and the solution treatment step is the one that blisters gas-bearing castings. Welding afterwards introduces a heat-affected zone into metal that was previously in the T6 condition, and that zone loses T6 strength; the squeeze casting design guide lists the related design rules for T6 and welded parts. A temper designation alone is not evidence of what the part will do, and T6 is not a quality grade; qualification on representative parts is what shows whether the section you care about meets its requirement.

Three habits follow for design. Place welds away from the highest-stressed section wherever the geometry allows, and treat the joint as a local reduction in properties rather than a continuation of the parent metal. State properties by section with specimen locations, because a separately cast test bar does not represent a thick boss in the part. Agree the weld procedure and any post-weld treatment with the design authority — the casting supplier can describe what the casting supports, but the welded joint is defined by the drawing and the fabricator, not assumed.

Published A356-T6 squeeze-cast reference values are 260–320 MPa tensile and 220–260 MPa yield; these are reference values, not acceptance criteria (company-reported), and elongation and hardness for squeeze-cast A356-T6 are not yet published. Guaranteed minimums come only from the named standard or specification measured on its specimen type, or from minimums agreed for the part with a defined specimen location — the A356-T6 casting specification explains that distinction.

What to put on the drawing and RFQ for a welded casting

The inputs below mirror what buyers already send on structural work, where the RFQ carries load case, weld locations and properties by section; see the RFQ inputs for automotive structural castings for the full pattern.

1. Weld locations shown on the drawing, not implied by the model.
2. Alloy named explicitly with the governing standard; A356 and A356.2 have different composition windows and are not interchangeable without checking the drawing.
3. Material specification and condition stated on the drawing and in the RFQ.
4. Properties by section with specimen locations for any load path that matters, plus load case and stiffness if the part is structural.
5. Machining sequence: which bores and sealing faces are finish machined after T6, and in which condition final dimensions are checked. For critical bores close to a weld, finish machining after welding is the usual design rule; agree it on the drawing.
6. Flatness-critical faces flagged, so quench distortion is planned for rather than discovered.
7. X-ray of the zones that matter functionally, with the discontinuity limit and reference standard agreed before the first sample.
8. Leak-rate requirement if the part is sealed.
9. The drawing note "No repair welding or impregnation without written approval."
10. The weld procedure (if any) and which party performs the welding, agreed per project.
11. Submission level and customer-specific requirements, with mandatory acceptance criteria separated from preferences.

Production welding vs repair welding of casting defects

A designed joint — a weld location shown on the drawing and covered by the load case and validation plan — is a different thing from repairing a casting defect. Repair welding of a foundry discontinuity should be treated as a deviation unless it is covered by an approved repair procedure and written approval, and drawings control it through the note "No repair welding or impregnation without written approval." Where a casting is porous in a region that matters, the cleaner route is normally a process decision at review stage, since squeeze casting is the option to review when a part needs T6 or welding or has failed a leak test as a die casting.

Trailer, marine and structural examples

Published CEX projects in this family are A356.2-T6 squeeze castings; further examples are collected in published squeeze casting conversions.

• Trailer bracket, A356.2-T6 squeeze cast, replaced a sand casting; it is weldable, with about 50% higher strength and markedly higher production efficiency reported (company-reported).
• Trailer connector, A356.2-T6 squeeze cast, replaced a steel casting with at least 54% weight reduction reported; it was a redesign (company-reported).
• Trailer beam, A356.2-T6, replaced steel and is produced as one casting, with substantial weight reduction reported (company-reported).
• Boat part, A356.2-T6 squeeze cast, replaced HPDC, with at least 50% higher strength reported (company-reported).

Each of these is a published outcome, not a rule, and every new part needs its own drawing review and validation. A steel-to-aluminum move is a design change rather than a material swap: aluminum has a lower elastic modulus, so bending stiffness must be checked and sections usually become deeper or differently ribbed; bolt bearing, thread engagement and galvanic isolation all change; fatigue, duty cycle, temperature and corrosion are re-checked; and validation runs on the finished part.

What CEX can and cannot confirm

In-house scope in Qingdao covers tooling, melting, casting, T6 heat treatment, CNC machining, finishing and inspection. Inspection equipment includes automatic CMM, video measuring, optical emission spectrometer, tensile testing machine, hardness tester, X-ray, helium leak detection and water immersion, and hardness after heat treatment is among the checks offered. Aluminum squeeze casting has been developed in-house since 2015 (company-reported), originally in response to porosity and shrinkage defects seen repeatedly in conventional HPDC — leaks, fractures, reduced service life and parts that could not be welded.

Two limits should be stated plainly. Welding is not listed in the published in-house scope, so the weld procedure and the welding responsibility have to be agreed per project, and buyers should write both into the RFQ. And the IATF 16949:2016 certificate 0494978 covers manufacturing of aluminium alloy die-cast parts, with clause 8.3 product design excluded and validity to 2027-01-07; design authority stays with the customer. Beyond that, regions to inspect, test sensitivity, discontinuity limits and any leak rate are agreed for the actual part rather than promised in general, as described on the inspection and leak testing page.