A356-T6 squeeze castings routinely hit 290-310 MPa ultimate tensile strength with 8-12% elongation, against 262 MPa and roughly 5% for the same alloy poured by conventional gravity permanent mold [S6]. That spread is the headline number a process engineer quotes when justifying a squeeze casting cell versus a green-sand or tilt-pour line.
The reason is microstructural: applied pressure during solidification collapses the gas porosity and shrinkage cavities that drag down ductility in gravity-poured A356, so the T6 temper can be developed on a near-pore-free matrix. The mechanical envelope below is what the data actually supports, with permanent-mold T6 sitting at 255 MPa UTS / 180 MPa yield / 5% elongation as the floor [S1], and squeeze-cast T6 reaching the upper end of the ASM-published A356.0 range, namely 200-300 MPa UTS with yield scaled accordingly [S3].
Property range by casting process and temper
Mechanical property of A356 tracks the casting process more than the alloy chemistry, because Fe-intermetallates, porosity, and dendrite arm spacing set the failure strain. Permanent-mold T6 typically delivers 255 MPa UTS, 180 MPa yield (0.2% offset), 5% elongation, and 70-100 Brinell hardness with a 500-kgf load and 10-mm ball [S1]. Sand-cast A356.0-T6 settles lower at 234 MPa UTS, 165 MPa yield, with density 2.67 g/cc [S5]. Squeeze-cast A356-T6 climbs to 290-310 MPa UTS at 8-12% elongation [S6], which is the same ballpark found in the A356.0-T6 ASM table, where the alloy's UTS window of 200-300 MPa (30-45 ksi) is achieved by Mg level and heat treatment tuning [S3]. For reference, a Metal Exchange side-by-side lists as-cast at ~230 MPa UTS / ~130 MPa yield / ~3.5% elongation versus T6 at ~310 MPa / ~230 MPa / ~7.0%, with density 2.68 g/cc and thermal conductivity ~155 W/m·K [S4]; a separately published A356 buyer guide quotes a T6 UTS band of 250-310 MPa (36-45 ksi), roughly a 50% jump over the as-cast 160-230 MPa (23-33 ksi) baseline [S7].
Why squeeze casting moves both strength and ductility
Pressurised solidification (typically 50-150 MPa on the liquid) suppresses gas nucleation and feeds shrinkage, so the as-cast soundness of A356 squeeze castings already approaches wrought density. The T6 temper then solutionises Mg2Si at roughly 540 °C, quenches, and artificially ages at around 155-175 °C, which precipitates fine β'' Mg2Si that pins dislocations. Yang et al. characterised the tension-compression response of A356-T6 and confirmed that, once porosity is removed, the alloy exhibits the symmetric, near-elastic-plastic behaviour you would expect from a heat-treated Al-Si-Mg casting rather than a pore-dominated one [S2]. A356 squeeze-castings tested in T5 show tensile and yield strength rising continuously with hold time at 160 °C up to 48 h, which sets a practical upper bound on ageing without inviting over-ageing softening [S8].
Selection criteria: is squeeze-cast A356-T6 the right pick?
Squeeze-cast A356-T6 is the right choice when the part needs both fatigue life and ductility beyond what gravity permanent mold can give, for example structural knuckles, suspension arms, brake calipers, aerospace housings, and pump or valve bodies where pressure tightness is mandatory. It is NOT the right choice when (a) the section exceeds what a squeeze press can clamp, (b) the geometry needs draft-free surfaces that only high-pressure die casting can deliver, or (c) the cost model cannot absorb the longer cycle time versus a 2000-ton cold chamber HPDC cell producing thin-wall A380 or A390 parts (see the shot weight and clamping force reference for 2000-ton cold chamber HPDC for comparison on the die-casting end of the spectrum). Against a sand-cast baseline of 234 MPa / 165 MPa [S5], squeeze-cast A356-T6 buys roughly 25-30% more UTS and 50-100% more elongation at a tooling cost between sand and HPDC.
Comparison of A356-T6 process routes against four decision criteria
Process selection reduces to four decision criteria: ultimate tensile strength, elongation, soundness / pressure tightness, and unit cost at volume. Sand-cast A356.0-T6 anchors the bottom of the strength axis at 234 MPa UTS with limited elongation (typically 2-4%) and visible microporosity [S5]. Permanent-mold T6 moves to 255 MPa UTS, 180 MPa yield, 5% elongation, 70-100 BHN, and is the workhorse for moderate-volume structural castings [S1]. Squeeze-cast T6 reaches 290-310 MPa UTS at 8-12% elongation and is near-net-shape pore-free, which is why it is specified for safety-critical automotive and aerospace nodes [S6]. On the high-volume end, HPDC A380 or A383 trades peak tensile strength (typically 290-330 MPa in as-cast, less after T6 because of blister risk) for sub-1-minute cycle times; that is a different decision tree entirely. The reference page on squeeze casting machines is useful for mapping clamp tonnage and shot sleeve options when sizing a cell for A356-T6 production.
Verification: tensile test method and quality control
Any of the UTS and elongation numbers above are only as good as the test specimen and heat-treat record. Specimens should be machined from the cast coupon per ASTM B557 (or the equivalent ISO 6892 series for metallic materials), with elongation measured over a 2-inch or 4× diameter gauge length to match the conventions used by permanent-mold baseline data [S1]. When comparing in-house data against the squeeze-cast 290-310 MPa / 8-12% envelope [S6], run a tensile testing machine class of at least ASTM E8 grade, and verify Mg content inside the 0.25-0.45% A356 window [S4] because tensile strength scales with Mg2Si fraction and under-alloyed heats will not reach the upper band even after a correct T6 cycle. For T5 / T6 time-at-temperature audits, the published ageing curve on cast A356 shows 160 °C holds to 48 h increasing tensile and yield strength monotonically before over-ageing kicks in, so any in-house data landing above 310 MPa is suspect until the temperature uniformity of the aging furnace is rechecked [S8].
Limitations, failure modes, and traceability
Three failure modes dominate when A356-T6 squeeze castings miss the property window. First, residual porosity from inadequate specific pressure or poor die venting drags elongation below 6% even when UTS is acceptable; this shows up as fish-eye fractures on the tensile fracture surface. Second, iron pickup above the 0.2% A356 ceiling [S4] forms β-Al5FeSi platelets that notch the matrix, costing elongation faster than strength. Third, incorrect solution treatment temperature (above ~555 °C) incipiently melts the Al-Mg2Si eutectic and gives a coarse-grained, low-ductility casting that no amount of aging will fix. None of these modes are visible on a tensile curve alone; microstructure and chemistry must be audited alongside the strength data. Buyers sourcing safety-critical squeeze-cast A356-T6 components should request the per-heat chemistry, the T6 cycle chart, and a tensile sample from a separately cast witness coupon, not just a mill cert.
A practical next step is to lock a single set of acceptance numbers in the part print before sourcing, for example A356-T6 with UTS in the 290–310 MPa range, elongation ≥ 8%, Fe ≤ 0.2%, and Mg 0.25–0.45% [S6][S4]. A trackable signal to watch in the next sourcing cycle is whether the foundry publishes squeeze-cast tensile data at multiple section thicknesses, since heavy-section A356-T6 drops back toward the permanent-mold band as cooling rate slows, and that band sits in the same 200-300 MPa UTS window the ASM handbook records for A356.0 [S3].
The underlying component specifications are covered under cast iron.