A390 Aluminum Alloy -Maximum Wear Resistance

A390 is a hypereutectic aluminum-silicon alloy containing approximately 17% silicon -well above the eutectic point of 12.6%. At this composition, large primary silicon crystals (hardness ~1,000 HV, comparable to carborundum) precipitate throughout the aluminum matrix before the eutectic solidifies, creating a composite microstructure with exceptional wear resistance and low thermal expansion.

A390 is specified when the casting surface itself must resist abrasive wear: cylinder liners, piston bore surfaces, clutch drum surfaces, and high-load sliding interfaces.

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Chemical Composition

Element	Min %	Max %
Silicon (Si)	16.0	18.0
Copper (Cu)	4.0	5.0
Magnesium (Mg)	0.45	0.65
Iron (Fe)	-	1.3
Zinc (Zn)	-	0.10
Manganese (Mn)	-	0.10
Aluminum (Al)	Balance	-

Per ASTM B85

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Mechanical Properties

Property	A390	A380 (reference)
Tensile strength	280 MPa	317 MPa
Yield strength	240 MPa	159 MPa
Elongation	<1% (very brittle)	3.5%
Hardness	120 HRB	80 HRB

A390 is hard and brittle -not a structural alloy. It is specified purely for wear resistance at the casting surface.

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Physical Properties

Property	A390	A380
Density	2.73 g/cm³	2.71 g/cm³
Thermal conductivity	134 W/m·K	96 W/m·K
Thermal expansion	18.0 μm/m·°C	21.1 μm/m·°C
Casting temperature	700-760°C	620-680°C

A390's low thermal expansion (18 vs 21 μm/m·°C for A380) is important for engine components where thermal growth affects piston and bore clearances.

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Why A390 Has Superior Wear Resistance

Abrasive wear resistance: Primary silicon crystals (16-18 vol% at 17% silicon) are harder than most metallic abrasives. They support contact load and resist penetration while the softer aluminum matrix deforms.

Adhesive wear resistance: Silicon crystals interrupt aluminum-to-aluminum contact continuity, preventing galling -the adhesive junction formation that destroys aluminum-on-aluminum sliding surfaces.

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Machining A390

A390's high silicon content requires specialized machining:

• PCD tooling mandatory: Polycrystalline diamond tools for boring, turning, and milling. Carbide tools wear too rapidly for production economics.
• Lower cutting speeds than standard aluminum; dry machining preferred.
• Honing: Bore surface finishing with diamond or SiC stones to achieve Ra 0.4-0.8 μm cross-hatch pattern for engine applications.

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Applications

Primary -Engine Components

• Aluminum cylinder liners (replacing cast iron in aluminum engine blocks)
• Piston bore surfaces in aluminum compressor cylinders
• Rotary engine housing bores
• Two-stroke engine cylinder bores

Secondary -Wear Surfaces

• Clutch drum and bell housing wear surfaces
• Brake drum surfaces in lightweight systems
• Scroll compressor body wear surfaces
• High-load bushing and sleeve applications

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A390 vs Other Aluminum Die Casting Alloys

A390 is not interchangeable with A380 or A413. It occupies a narrow niche: applications where the casting surface must resist sustained abrasive or adhesive wear. For all other applications, A380 provides better overall properties at lower cost.

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A390 inquiry: yaoqingpu1983@gmail.com | +86 138 1403 4409 | No.6, Rungu Road, Nanjing, China

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A390 vs Other Aluminum Alloys -When to Specify

A390 is not an all-purpose alloy. It has a specific role -maximum wear resistance at the casting surface -and is specified only when that role is the primary design requirement.

Property	A390	A380	A413
Tensile strength	280 MPa	317 MPa	290 MPa
Hardness	120 HRB	80 HRB	80 HRB
Elongation	<1%	3.5%	2.5%
Thermal conductivity	134 W/m·K	96 W/m·K	121 W/m·K
Thermal expansion	18.0 μm/m·°C	21.1 μm/m·°C	20.0 μm/m·°C
Castability	Difficult	Excellent	Excellent
Machinability	Requires PCD tooling	Excellent	Good
Pressure tightness	Poor	Good	Best
Wear resistance	Best	Moderate	Moderate

Never specify A390 for:

• Structural brackets or housings -brittle (<1% elongation), fractures under impact
• Pressure-tight applications -high silicon creates porosity problems
• Any application requiring welding -extremely poor weldability
• Programs requiring extensive machining with standard carbide tooling -economically unacceptable tool wear

Always specify A390 for:

• Cylinder liner applications where wear resistance is the sole design criterion
• Applications where the casting surface itself is the wear surface and secondary coating is not an option

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Casting Challenges for A390

A390's hypereutectic silicon content (17%) creates processing challenges that do not exist with standard die casting alloys:

Primary silicon precipitation control: At 17% silicon, large primary silicon crystals precipitate from the melt during cooling before the eutectic solidifies. If these crystals are too large (>50 μm), they create coarse surface texture on the wear surface and reduce machinability. Phosphorus additions (0.01-0.03%) to the melt refine the primary silicon crystals to <20 μm, improving both surface quality and machinability.

Higher casting temperature: A390 requires casting at 700-760°C -higher than A380's 620-680°C. This increases thermal load on the die and accelerates die wear, reducing die life by approximately 30-40% versus A380 programs.

Increased die soldering risk: The high silicon content reduces A390's die soldering resistance compared to A380. Die lubrication management and gate velocity control are more critical for A390 programs.

Honing and surface preparation: After machining, A390 cylinder bore surfaces require honing to expose the primary silicon particles at the bore surface. The honed surface -silicon particles proud of the aluminum matrix, forming a wear-resistant plateau -is the functional feature that provides A390's wear performance. This final honing step requires diamond or SiC stones and a specific honing pattern (typically 30-35° cross-hatch angle for engine applications).

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A390 in Modern Automotive Engines

Aluminum engine blocks with A390 cylinder bores represent the most technically demanding A390 die casting application. A modern 4-cylinder aluminum engine block with A390 cylinder bores:

• Provides the wear resistance of cast iron cylinder liners at aluminum's density advantage
• Enables the bore-to-bore proximity that allows smaller engine packaging
• Reduces block mass by 25-35% versus equivalent cast iron bore block designs

These engine blocks are produced by specialized A390 die casting cells with phosphorus treatment of the melt, controlled die temperature management, and dedicated honing equipment -not standard aluminum HPDC production. KastMfg produces A390 cylinder liner inserts and bore section castings for customers bringing integrated cylinder block capability.

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Physical Properties Summary

Property	Value	Significance
Thermal conductivity	134 W/m·K (+39% vs A380)	Better heat dissipation from bore surface
Thermal expansion	18.0 μm/m·°C (-5% vs A380)	Better bore clearance stability across temperature
Density	2.73 g/cm³	Essentially same as A380
Hardness	120 HRB	Exceeds hardened steel's surface hardness capability

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A390 inquiry: yaoqingpu1983@gmail.com | +86 138 1403 4409 | No.6, Rungu Road, Nanjing, China