What Are the Differences Between Aluminum Alloy Die Casting and Gravity Casting in Automotive Components?
Aluminum alloy die casting and Gravity Casting exhibit significant differences in automotive applications due to variations in process principles and performance characteristics.
Below is a detailed comparison across process features, mechanical properties, costs, and typical applications:
I. Comparison of Process Principles and Production Features
| Aspect | Aluminum Alloy Die Casting | Aluminum Alloy Gravity Casting |
| Process Principle | High pressure (500–1,000 MPa) injects molten aluminum into molds for rapid cooling and forming. | Relies on gravity to fill molds, with natural cooling or low-speed auxiliary pressure. |
| Production Efficiency | Short cycle (seconds to tens of seconds), suitable for mass automated production. | Longer cycle (minutes to tens of minutes), lower efficiency than die casting. |
| Mold Requirements | High-cost, heat-resistant alloy molds (e.g., H13 steel) to withstand high pressure. | Simpler molds, lower cost, and suitable for small- to medium-batch production. |
| Dimensional Accuracy | High precision (IT12–IT13), smooth surface (Ra 1.6–3.2 µm), can form complex thin walls (0.5–5 mm). | Lower precision (IT14–IT16), rougher surface, better for thicker walls (≥3 mm). |
| Internal Defects | High-speed filling may trap gas, resulting in porosity, and is therefore unsuitable for high-pressure sealing parts. | Slow filling allows gas escape, denser microstructure, and fewer defects. |
| Aspect | Aluminum Alloy Die Casting | Aluminum Alloy Gravity Casting |
| Alloy Types | High-silicon alloys (e.g., ADC12, A380; Si 8–12%) for better flowability. | Heat-treatable alloys (e.g., A356, A357, Al-Cu series). |
| Mechanical Properties | - Tensile strength: 200–350 MPa<br>- Elongation: 1–5%<br>- Hardness: 60–100 HB<br>(Fine grains but porosity reduces toughness.) | - Tensile strength: 250–400 MPa<br>- Elongation: 5–15%<br>- Hardness: 70–120 HB<br>(T6 heat treatment improves strength/ductility.) |
| Microstructure | Dense surface but potential micropores; heat treatment unsuitable (pore expansion causes warping). | Coarser but uniform grains; heat/pore refinement improves properties. |
| Corrosion Resistance | Good surface density resists corrosion, but internal pores may reduce long-term reliability. | Uniform structure; corrosion resistance depends on alloy/heat treatment. |
| Aspect | Aluminum Alloy Die Casting | Aluminum Alloy Gravity Casting |
| Mold Cost | High (complex, high-pressure molds); cost-effective for mass production (≥100k units). | Low (simple molds); suited for small/medium batches (1k–100k units) or prototypes. |
| Unit Production Cost | Low (high efficiency, minimal waste), but high equipment costs (die-casting machines). | Higher (longer cycles, manual labor), lower equipment investment. |
| Post-Processing | Easy surface treatment (plating/painting); minimal machining needed. Internal defects hard to repair. | May require machining to remove defects; added heat treatment costs (e.g., T6). |
- Die Casting Applications:
Engine Systems: Valve covers, oil pans (lightweight, heat dissipation); turbocharger housings (A356-T6 for high temp).
Transmission/Drivetrain: Gearbox housings (precision molding), clutch housings (lightweight).
Body Structures: Integrated rear floor castings (e.g., Tesla Model Y); door frames, bumper brackets (thin-wall strength).
Chassis/Suspension: Steering knuckles, control arms (porosity control for strength); brake calipers (heat dissipation).
- Gravity Casting Applications:
Chassis Load-Bearing Parts: Wheels (A356-T6 for impact resistance); suspension brackets/subframes (dynamic loads).
Engine Core Components: Cylinder blocks (heat-treated A356-T6 for wear resistance); cylinder heads (high-pressure/temp).
Safety Components: Crash beams, A/B-pillar reinforcements (heat-treated for collision strength); battery housings (corrosion resistance).
V. Selection Guidelines
Prefer Die Casting for high-volume, lightweight, precision parts (e.g., housings, structural components) where porosity is acceptable (non-critical/non-pressure areas).
Prefer Gravity Casting for high-strength, high-toughness, or heat-treatable parts (e.g., wheels, engine blocks), or for small-to-medium batches.
VI. Case Studies:
Tesla Model 3 motor housing: Die-cast for lightweight efficiency.
Porsche 911 wheels: Gravity-cast A356-T6 for high-speed safety.
VII. Application Differences in the New Energy Vehicle Sector
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- Comparison of Battery System Components
Aluminum Die Casting Applications:
- Comparison of Battery System Components
- Battery Pack Cover Plate: A383 alloy (conductivity ≤25% IACS) is used, balancing electromagnetic shielding and lightweighting with high forming efficiency (3-5 parts/minute). A typical failure case: IP67 sealing failure in a vehicle model due to die-casting porosity.
- Battery Module End Plate: High-thermal-conductivity ADC12 alloy is employed, with die-cast 1.2mm thin-wall cooling ribs, but prone to cracking along porosity zones during collisions.
Aluminum Gravity Casting Applications:
- Battery Tray Assembly: A356-T6 is selected, achieving a tensile strength of 310MPa after T6 heat treatment, with 40% less welding distortion compared to die-cast parts. A typical failure: coolant leakage in a liquid cooling plate due to casting shrinkage porosity in a manufacturer.
- High-Voltage Junction Box Housing alloy is used, with X-ray inspection showing a 15% higher hermetic compliance rate than die-casting.
- Comparison of E-Drive Systems
Advantages of Aluminum Die Casting:
- Comparison of E-Drive Systems
- Motor Housing: A360 alloy die casting can form ultra-thin 0.8mm cooling fins, but the high-speed rotor mounting surface requires secondary machining to ensure concentricity.
- Reducer Housing: Vacuum die-casting technology (porosity ≤1%) replaces cast iron, reducing weight by 35%.
Special Applications of Aluminum Gravity Casting:
- Inverter Cooling Housing: A357-T6 casting + CNC machining delivers stable thermal conductivity of 160 W/(m·K), with better batch consistency than die-casting.
- Motor End Cover: Gravity casting + local squeeze strengthening increases axial load capacity by 20% over die-casting; an 800V motor passed a 2 million-cycle durability test.
- Emerging Material Technologies
Die-Casting Breakthroughs:
- Emerging Material Technologies
- High-vacuum die-casting (<5kPa) for battery structural components reduces porosity to below 0.5%.
- Al-Mg-Sc alloy die-cast motor housings achieve a yield strength of 280MPa.
Gravity Casting Innovations:
- Gradient pressure casting resolves cold shut defects in battery trays >1.5m.
- Nano-modification treatment increases A356 alloy elongation to 18%, suitable for flexible circuit brackets.
- Industry Failure Data Analysis (2020–2023)
| Primary Failure Cause | Die-Cast Parts (%) | Gravity Cast Parts (%) |
| Sealing failure due to porosity | 67% | – |
| Stress corrosion from improper heat treatment | – | 82% |