A356 Aluminum Casting - Properties, T6 & Uses

A356 (AlSi7Mg0.3) is the most widely specified aluminum casting alloy for structural and pressure-tight applications. Its 7% silicon and 0.3% magnesium combination delivers an unmatched balance of castability, ductility, and heat-treatable strength - which is why wheels, chassis brackets, and aerospace fittings default to A356 with T6 heat treatment.

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A356 Chemical Composition

Element	Nominal %	Range
Silicon (Si)	7.0	6.5 to 7.5
Magnesium (Mg)	0.30	0.25 to 0.45
Iron (Fe)	-	0.20 max
Copper (Cu)	-	0.20 max
Titanium (Ti)	0.15	0.20 max (grain refiner)
Aluminum (Al)	Balance	-

The very low iron content (0.20% max vs A380's 1.3%) is the defining feature - it gives A356 its ductility, but it is also why A356 is rarely used in high-pressure die casting (see below).

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Mechanical Properties (A356-T6)

Property	A356-T6	A380 (HPDC)
Tensile strength	260 to 310 MPa	320 MPa
Yield strength	200 to 270 MPa	160 MPa
Elongation	3 to 8%	3.5%
Hardness	70 to 100 HB	80 HB
Fatigue strength	90 MPa	140 MPa (not heat treated)

A356-T6's elongation of 3 to 8% is roughly double that of standard die casting alloys in good sections - the key reason structural and safety-critical parts specify it.

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Why A356 Is Rarely High-Pressure Die Cast

Buyers frequently ask for "A356 die casting." Technically it can be done, but two factors work against it:

1. Process fit. A356 is a heat-treatable structural alloy designed for sand, permanent mold, and low-pressure processes. Its value is in T6-treated ductility - properties that HPDC's fast, turbulent fill does not need and cannot fully use.
2. Die soldering tendency. A356's low iron content (HPDC alloys like A380 carry 0.8 to 1.3% iron partly to protect the die) increases the alloy's tendency to solder to H13 die steel, cutting tool life. Combined with HPDC's thin-wall economics, A356 in HPDC rarely makes sense.

Practical guidance: if the part needs HPDC economics, specify A380 or ADC12. If it needs A356's ductility and T6 strength, use gravity die casting or low pressure die casting - the processes A356 was designed for.

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A356 Variants

Variant	Difference	Used For
A356.0	Base alloy	General structural castings
A356.1 / A356.2	Lower iron (0.12% max) and tighter trace-element limits	Premium aerospace and safety parts
F357 / A357	Beryllium-added, higher strength	Aerospace fittings
A355	Older cousin - lower Si (5%), higher Cu (1.5%); T6 strong but less ductile than A356	Legacy aerospace drawings, sand castings

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T6 Heat Treatment for A356

The T6 cycle is what unlocks A356's properties:

1. Solution treatment: 535°C for 6 to 12 hours - dissolves Mg2Si into the matrix
2. Quench: warm water (60 to 80°C) to limit distortion
3. Artificial aging: 155°C for 3 to 5 hours - precipitates strengthening Mg2Si

KastMfg manages T6 cycles with distortion-controlled fixturing for machined datums, and verifies hardness per casting batch. See our heat treatment service for process detail.

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Applications

• Automotive and EV structural brackets, subframes, suspension knuckles
• Wheel and hub castings
• Pump and valve bodies requiring pressure tightness
• Aerospace and drone structural fittings
• Robotic arm links and automation frames
• Marine hardware (with appropriate coating)

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A356 vs A380 - Selection Table

Requirement	Choose A356 (gravity/LPDC)	Choose A380 (HPDC)
Elongation above 5%	Yes	-
T6 heat treatment	Yes	Not recommended (blister risk)
Thin walls under 2 mm	-	Yes
Volume above 50k/year, small parts	-	Yes
Weldability	Yes	Limited
Pressure tightness + structural load	Yes	Case by case

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Frequently Asked Questions

Can A356 be die cast at all?

Yes, with modified tooling (special die steel surface treatments, aggressive thermal management) and typically with vacuum assist, but die life drops significantly versus A380. For most programs, switching the process (gravity/LPDC) is more economical than forcing A356 into HPDC.

What is the difference between A356 and A356.2?

Iron and trace-element limits. A356.2 restricts iron to 0.12% maximum with tighter impurity control, producing the highest ductility and fatigue performance. It is the default for aerospace and premium wheel programs.

Does A356 need heat treatment?

For structural use, yes - as-cast A356 (F temper) only reaches about 170 MPa tensile. T6 roughly doubles yield strength. Non-structural housings can run F or T5 temper to save cost.

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Related Materials

• die casting materials - full alloy selection guide
• A380 aluminum die casting - the HPDC workhorse
• ADC12 die casting - the JIS equivalent of A383
• aluminum die casting - KastMfg HPDC capability
• aerospace die casting - where A356's T6 ductility matters most

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A356 casting inquiry: yaoqingpu1983@gmail.com | +86 138 1403 4409 | No.6, Rungu Road, Nanjing, China