Die Casting Heat Treatment - T5 and T6 Explained

Heat treatment of aluminum die castings can increase tensile strength by 20-30% and yield strength by 40-50% over as-cast values -without changing geometry or adding weight. For structural, load-bearing, or safety-critical castings, heat treatment is often the difference between meeting and failing the mechanical property specification.

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Aluminum Heat Treatment Designations

Temper	Name	Process	Effect
F	As fabricated	None	Baseline
T5	Artificially aged	Aging only -no solution treatment	Moderate strength improvement
T6	Solution + artificial age	Solution treat + quench + aging	Maximum strength
T7	Solution + overaged	Solution + extended aging	Stress-corrosion resistance

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T5 -Artificial Aging Only

Parts are placed in an aging oven at 150-175°C for 3- hours immediately after casting. Elevated temperature accelerates precipitation of strengthening phases from the supersaturated solid solution retained from casting.

T5 provides:

• Tensile strength +15-25% (A380-F: 317 MPa ->T5: ~350 MPa)
• Yield strength +30-40% (A380-F: 159 MPa ->T5: ~195 MPa)
• Hardness +10-20%
• Dimensional stability improvement (stress relief)

T5 advantages:

• No quench -no distortion from thermal shock
• 3- hours total -fast and low cost
• Applicable to standard HPDC parts without porosity concerns

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T6 -Solution Treatment + Artificial Aging

T6 delivers maximum mechanical property improvement through three stages:

Stage 1: Solution Treatment (480-540°C, 2-12 hours)

All strengthening precipitates dissolve into a uniform solid solution. The alloy is at its softest and most ductile.

Stage 2: Quench (water or forced air)

Rapid cooling freezes the supersaturated solid solution, trapping strengthening elements in solution.

Stage 3: Artificial Aging (150-175°C, 4-12 hours)

Controlled precipitation of fine coherent precipitates (CuAl2 Mg2Si) impedes dislocation movement -this is the strengthening mechanism.

T6 results (A380 example):

Property	F (as-cast)	T6 (VADC required)
Tensile strength	317 MPa	~360-380 MPa
Yield strength	159 MPa	~290-310 MPa
Elongation	3.5%	~4-%
Hardness	80 HRB	~88-112 HRB

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Why T6 Requires VADC

Standard HPDC aluminum contains gas porosity from turbulent injection. During solution treatment at 480-540°C, trapped gas expands -pushing thin wall sections outward as visible surface blisters. T6 on standard HPDC fails due to blistering.

Solutions:

1. VADC (Vacuum-Assisted Die Casting): Reduce gas porosity before casting. ASTM E505 Class 1- parts can be T6 treated without blistering -KastMfg's primary T6 path.
2. VPI before T6: Seal pores by vacuum pressure impregnation before heat treatment -suppresses expansion.
3. Low-pressure or gravity casting: Inherently lower porosity -no VADC required.

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Alloy T6 Response

Alloy	T5 Response	T6 Response	Notes
A380	Good	Good (VADC required)	Most common structural program
ADC12	Good	Good (VADC)	Automotive structural
A360	Moderate	Good (VADC)	Lower copper reduces response
A413	Poor	Poor	Near-eutectic; limited precipitate formers
A356 (LPDC/gravity)	Good	Excellent	Best T6 alloy -specialty program

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Heat Treatment Equipment at KastMfg

• Continuous belt furnaces for high-volume T5 programs (temperature uniformity ->5°C)
• Batch furnaces for T6 solution treatment
• Water quench tanks with temperature-controlled water (20-40°C for controlled quench rate)
• Aging ovens with programmable profiles

Third-party T6 treatment at certified partners available for programs requiring specific certifications.

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Heat treatment inquiry: casting@kastdiecast.com | +86 138 1403 4409 | No.6, Rungu Road, Nanjing, China

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