FAQ About Aluminum Die Casting

I. Basic Understanding

1. What is Aluminum Die Casting?

Aluminum die casting is a precision metal forming process. It involves injecting molten aluminum alloy into a pre-designed metal mold (die casting mold) under high pressure. After the alloy cools and solidifies, the mold is opened to remove the formed workpiece. Its core characteristics are high pressure (usually 10-150MPa) and high speed (filling speed up to 0.5-50m/s), enabling mass production of high-precision, complex-structured aluminum parts.

2. What are the core differences between aluminum die casting and other casting processes (such as sand casting and gravity casting)?

The core differences lie in forming pressure, precision, and efficiency:

• Pressure and Filling: Aluminum die casting uses high-pressure forced filling to fill complex cavities; sand casting and gravity casting rely on natural gravity filling, suitable for parts with simple structures.

• Precision and Surface Quality: Aluminum die castings have small dimensional tolerances (IT8-IT12) and low surface roughness (Ra1.6-6.3μm), requiring no extensive subsequent processing; sand castings have low precision and rough surfaces, needing multiple grinding processes.

• Efficiency and Batch Production: Aluminum die casting is suitable for mass production (single mold cycle as short as a few seconds to tens of seconds); sand casting has low mold costs but low production efficiency, suitable for small-batch, customized products.

3. What are the main advantages and limitations of aluminum die casting?

Advantages:

• Lightweight: Aluminum alloy has a low density (2.7g/cm³), about 35% lighter than steel, suitable for weight-sensitive scenarios (e.g., automotive, aerospace).

• High Strength: Through alloy proportioning and heat treatment, high strength and hardness can be achieved to meet the needs of structural parts.

• Precision Forming: Complex structures (such as holes, grooves, threads) can be integrally formed, reducing assembly processes.

• Cost-Effectiveness: Low unit cost in mass production with high material utilization rate (usually 80%-95%).

Limitations:

• High Mold Cost: Metal molds have a long manufacturing cycle (weeks to months) and high cost, not suitable for small-batch production (less than 1,000 pieces).

• Wall Thickness Limitation: Generally suitable for parts with a wall thickness of 0.5-5mm; excessive thickness is prone to shrinkage and porosity defects.

• Welding Difficulty: Some die castings have many internal pores, which may cause cracks and pores after welding, requiring special welding processes.

II. Process and Technology

1. What are the main types of aluminum die casting processes? What are their applicable scenarios?

• High-Pressure Die Casting (HPDC): The most mainstream process, featuring high-pressure and high-speed filling. Suitable for mass production of small and medium-sized precision parts (e.g., automotive transmission housings, electronic device casings), accounting for over 80% of total aluminum die castings.

• Low-Pressure Die Casting (LPDC): With low pressure (0.02-0.15MPa) and stable filling, it has fewer porosity defects. Suitable for producing high-quality, complex-loaded parts (e.g., engine cylinder heads, wheel hubs).

• Gravity Die Casting: Relies on gravity for filling, with lower mold costs than HPDC. Suitable for medium-batch, simple-structured parts (e.g., radiators, brackets).

2. What is the typical process flow of aluminum die casting?

Core Process: Mold Design and Manufacturing → Aluminum Alloy Melting (controlled temperature: 650-700℃) → Mold Preheating (150-300℃ to prevent rapid alloy cooling) → High-Pressure Filling (injecting molten aluminum alloy into the cavity) → Pressure Holding and Cooling (maintaining pressure until alloy solidification) → Mold Opening and Part Removal → Deburring/Flash Removal → Heat Treatment (optional) → Surface Treatment (optional) → Quality Inspection → Finished Product.

3. What are the common defects of die castings? How to avoid them?

• Porosity: Caused by gas absorption during alloy melting and excessive filling speed. Prevention methods: Degassing during melting (introducing nitrogen/argon), controlling filling speed, and optimizing mold venting channels.

• Shrinkage/Shrinkage Porosity: Caused by uneven cooling speed and insufficient pressure holding. Prevention methods: Optimizing the mold cooling system, extending pressure holding time, and adjusting alloy composition.

• Burrs/Flash: Caused by excessive mold clearance and insufficient clamping force. Prevention methods: Increasing clamping force, trimming the mold to adjust clearance, and optimizing die casting parameters.

• Cracks: Caused by improper alloy composition, rapid cooling speed, and unreasonable part structure. Prevention methods: Selecting appropriate aluminum alloy grades, optimizing mold cooling, and avoiding sharp corners/sudden wall thickness changes of parts.

III. Material Selection

1. What aluminum alloy grades are suitable for die casting? What are their characteristics and applications?

• ADC12 (Japanese standard, corresponding to domestic YL113): High silicon content (10%-13), excellent fluidity and formability, suitable for complex-structured parts (e.g., mobile phone middle frames, toy parts), but average corrosion resistance and medium strength.

• A380 (American standard): Excellent comprehensive performance, balanced fluidity, strength, and corrosion resistance, suitable for automotive parts (e.g., transmission housings, engine brackets) and industrial equipment accessories.

• A356 (American standard): High-purity aluminum alloy with high strength and good corrosion resistance. Its mechanical properties are significantly improved after T6 heat treatment, suitable for load-bearing parts (e.g., engine cylinder heads, wheel hubs).

• ADC10 (YL112): Performance similar to ADC12, slightly lower silicon content, and better toughness, suitable for complex parts with certain toughness requirements.

2. How to select the appropriate aluminum alloy grade according to product requirements?

Core Principle: Comprehensive judgment based on the product's force-bearing conditions, corrosion resistance requirements, structural complexity, batch quantity, and cost:

• Complex structure, mass production, low cost: Prioritize ADC12/A380 for good fluidity and easy forming.

• Complex force-bearing, high reliability: Select A356, whose strength meets structural part requirements after heat treatment.

• Corrosion-resistant scenarios (e.g., outdoor equipment): Optional A380 or special corrosion-resistant aluminum alloy, combined with surface treatment.

• Lightweight + high toughness: Low-silicon aluminum alloy or composite aluminum alloy materials can be used.

IV. Applications and Post-Treatment

1. In which industries are aluminum die castings mainly used?

Widely used in various fields:

• Automotive Industry: The largest proportion (about 40%), such as engine housings, transmission housings, instrument panel brackets, and door frames.

• Electronics and Electrical Appliances: Mobile phone/computer casings, radiators, power adapter casings, and home appliance bases.

• Industrial Equipment: Pump bodies, valve bodies, gearboxes, and sensor housings.

• Aerospace: Small structural parts and instrument panel components (meeting high strength and lightweight requirements).

• Medical Devices: Wheelchair parts and medical equipment casings (requiring corrosion resistance and precision forming).

2. What are the common surface treatment methods for aluminum die castings? What are their functions?

• Anodizing: Forms a hard oxide film, improving corrosion resistance, wear resistance, and aesthetics. It can be dyed (black, natural color, colored), suitable for decorative parts.

• Spraying (Powder Coating/Electrophoretic Coating): Covers a protective film, providing corrosion resistance and scratch resistance with a wide range of color options. Applied to outdoor equipment and home appliance casings.

• Electroplating: Nickel plating, chrome plating, etc., improving surface hardness and aesthetics, suitable for parts requiring conductivity or high gloss.

• Passivation Treatment: Forms a dense passivation film, enhancing corrosion resistance. Often used for parts requiring subsequent welding or assembly without affecting conductivity.

3. Can aluminum die castings be heat-treated?

Some can, but it depends on the aluminum alloy grade and defect conditions:

• Heat-Treatable Grades: Such as A356 and A357. After T6 heat treatment (solution treatment + artificial aging), the tensile strength can be increased by 30%-50%.

• Limitations: High-pressure die castings may have internal pores. Pore expansion during heat treatment can cause part deformation and cracking. Therefore, common die casting aluminum alloys such as ADC12 are generally not recommended for heat treatment, only low-temperature aging treatment is allowed.

V. Cost and Quality Inspection

1. What are the main factors affecting the cost of aluminum die casting?

• Mold Cost: The largest proportion (for small batches). Mold material (H13 steel), complexity, and precision directly determine the cost; complex molds can cost tens of thousands to hundreds of thousands of yuan.

• Material Cost: Affected by fluctuations in aluminum alloy ingot prices and material utilization rate (scrap rate).

• Production Batch: The larger the batch, the lower the unit mold cost allocation. Small batches (less than 500 pieces) may be uneconomical due to high mold costs.

• Process and Post-Treatment: Low-pressure die casting is more expensive than high-pressure die casting; complex post-treatment (such as anodizing and electroplating) adds additional costs.

2. What are the quality inspection methods for aluminum die castings?

• Visual Inspection: Checking surface defects (burrs, cracks, porosity, scratches) with the naked eye or magnifying glass.

• Dimensional Inspection: Using calipers, micrometers, projectors, and Coordinate Measuring Machines (CMM) to detect dimensional accuracy and geometric tolerances.

• Internal Defect Inspection: X-ray Testing (RT) and Ultrasonic Testing (UT) for internal porosity, shrinkage, and cracks; Penetrant Testing (PT) and Magnetic Particle Testing (MT) for surface and near-surface defects.

• Mechanical Property Testing: Tensile testing and hardness testing (Brinell, Rockwell) to detect tensile strength, hardness, and other indicators.

• Composition Analysis: Using a spectrometer to detect whether the aluminum alloy composition meets standards.

VI. Environmental Protection and Compliance

1. How to achieve environmental compliance in the aluminum die casting production process?

• Waste Gas Treatment: Smoke and harmful gases (such as sulfur dioxide) generated during melting must be treated by gas collection devices + waste gas purification equipment (activated carbon adsorption, bag dust removal) before emission.

• Waste Water Treatment: Cooling water and cleaning wastewater must undergo sedimentation, filtration, and neutralization treatment, and be discharged or recycled only after meeting emission standards.

• Solid Waste Recycling: Waste aluminum slag, waste molds, and defective products can be recycled to reduce solid waste emissions; waste cutting fluid and lubricating oil must be handled by professional institutions to avoid pollution.

• Energy Conservation Optimization: Using energy-saving melting furnaces and waste heat recovery systems to reduce energy consumption; optimizing die casting parameters to reduce scrap rate and improve resource utilization.

2. Do aluminum die castings comply with environmental standards such as RoHS and REACH?

Yes, provided that compliant aluminum alloy materials and surface treatment processes are selected:

• Aluminum alloy itself does not contain prohibited substances such as lead and mercury, meeting RoHS standards.

• During surface treatment, the content of harmful substances in coatings and electroplating solutions must be controlled to avoid exceeding REACH regulation limits.

• Formal manufacturers will provide environmental testing reports to ensure products meet the environmental requirements of the target market.