Aluminum casting is a common and efficient manufacturing process for producing a variety of custom parts with complex structures and high-performance requirements. The entire process covers part design, casting method selection, mold development, metal melting and pouring, post-processing, and surface treatment. Each step directly affects the dimensional accuracy, mechanical properties, and consistency of the product.
This guide covers various aluminum casting methods, general process flow, cast aluminum selection, common defects and solutions, post-processing methods, and how CEX Casting improves casting quality through advanced technology. Please read on to choose the aluminum casting method that is right for you.
Aluminum Casting Methods
Sand Casting
Sand casting is suitable for producing small batches of aluminum castings with large sizes or complex structures.
This method is low-cost and flexible in design, but the surface is rough. It is usually used for early prototype development or industrial machinery parts.
Die Casting
High-pressure die casting involves injecting molten aluminum into steel molds under high pressure.
It is suitable for the mass production of small aluminum alloy die casting components with complex structures and precision requirements.
Gravity Casting
Use gravity to fill molten aluminum into a permanent mold, and the surface of the produced parts is better than sand casting.
Suitable for medium-volume production, and for parts that require strength and precision.
Investment Casting
Investment casting uses wax molds and ceramic shells to achieve high-precision molding effects.
It is very suitable for small, complex aluminum castings. Although the cost is higher, the dimensional accuracy and surface quality are excellent.
Low-Pressure Casting
This method uses controlled air pressure to push molten aluminum into the mold, and the casting can obtain higher density and reduce internal pores.
Widely used in the manufacture of structural parts in the automotive and aviation fields.
Aluminum Casting Process
Part Design
Use professional modeling software such as SolidWorks and Pro/E for 3D modeling, set a reasonable draft angle (usually 1°–3°), and use rounded corners to reduce stress concentration.
It is recommended to simulate the flow and solidification of aluminum liquid during the modeling stage to identify potential defects such as insufficient filling and hot spots in advance.
Casting Method Selection
The process selection needs to be combined with the complexity of the part structure, precision requirements, order volume, and cost control.
Different processes have different adaptability to wall thickness, shape, and cooling methods, which should be determined after DFM manufacturability analysis.
Mold Preparation
The mold system includes the cavity, runner, exhaust channel, riser, and cooling system.
The flow path, pressure balance, and solidification sequence should be considered in the design.
Common mold types include steel molds (for die casting and gravity casting), ceramic shells (for investment casting), and resin sand molds (for sand casting).
The mold should be preheated before casting to prevent metal cold shut, shrinkage, or sticking.
Aluminum Alloy Melting
Aluminum alloys are usually heated to 680–720°C in an induction furnace or resistance furnace.
Refining agents should be used to remove oxides during melting. Argon or nitrogen should also be used for degassing to reduce hydrogen content.
Aluminum Pouring
The pouring method varies depending on the casting process. High-pressure die casting uses high-pressure filling to reduce shrinkage and pores.
Gravity casting uses tilted pouring to help control the flow rate and reduce turbulence.
No matter which process is used, the pouring process should be continuous and stable to avoid splashing, secondary oxidation, and air entrainment.
Cooling and Solidification
Controlling the cooling rate is essential to obtain a fine-grained structure.
Chilled iron should be used to promote directional solidification. Properly designed risers can prevent shrinkage or internal looseness.
Thermal node analysis and real-time temperature control devices can be installed in key areas to ensure uniform temperature drop.
Casting Removal
After the casting is cooled, it is demolded and removed mechanically or manually. Then, the process residues, such as gates, risers, and overflow edges, are cut off.
Post-Processing
Post processing includes sandblasting, tumbling, heat treatment, and CNC machining.
Carried out based on product requirements to improve dimensional accuracy and mechanical performance.
Surface Treatment
Common surface treatment methods include powder coating, spray painting, electroplating, electrophoresis, anodizing, etc., to enhance corrosion resistance, aesthetics, and wear resistance.
How to Choose the Right Aluminum Alloy
|
Alloy |
Characteristics | Application Scenarios |
|
A380 |
Good fluidity, high strength, low cost | Electronic product housing, automotive parts |
| A383 | Stronger corrosion resistance than A380 |
Thin-walled parts, high-pressure parts |
|
A360 |
High strength, good air tightness | High-load automotive applications |
| A413 | Excellent fluidity, good air tightness |
Pump body, hydraulic parts |
|
ADC12 |
Japanese standard, easy to process, easy to cast | Consumer electronics, automotive electronics |
| AlSi10Mg | High strength, heat treatable, excellent weldability |
Electric vehicle housing, radiator, structural parts |
|
AlSi9Mg |
High strength, good ductility, corrosion resistance | Cylinder heads, aerospace structural parts, engine brackets |
| AlSi7Mg | Corrosion resistance, heat treatable, good ductility |
Marine components, structural frames |
| AlSi9Cu3 | High strength, excellent air tightness |
Gearbox, transmission parts |
Common Casting Defects and Solutions
Porosity
Cause: The aluminum liquid contains gas (such as hydrogen) or entrains air during pouring.
The gas cannot escape during the cooling process, forming a round or oval cavity inside the casting.
Solution: Control the melting temperature, use refining agent or argon/nitrogen degassing, keep the aluminum liquid clean and avoid excessive agitation, and optimize the mold exhaust system to prevent gas stagnation.
Shrinkage Cavity
Cause: Aluminum shrinks in volume during solidification. If there is no effective shrinkage compensation, internal cavities will form in the hot spot or wall thickness area, usually located in the center of the casting or at the far end of the riser.
Solution: Reasonably set the riser and shrinkage compensation system, use a chiller to guide directional solidification, avoid the formation of internal areas in the casting that cannot be compensated, and optimize the thickness distribution of the casting.
Inclusions
Cause: The oxide film, slag, or foreign matter generated during the smelting process is mixed into the aluminum liquid, and after flowing into the mold cavity with the metal, it is retained in the casting, affecting the strength and density.
Solution: Keep the smelting environment clean, remove slag regularly, use a ceramic foam filter for fine filtration, and reduce the pouring speed to avoid rolling.
Cold Shut
Cause: When two streams of aluminum liquid meet in the mold, the temperature is too low, and they fail to fully fuse, forming obvious boundaries or crack-like defects, which often appear in the thin-walled area at the far end.
Solution: Increase the pouring temperature of aluminum liquid, preheat the mold to reduce heat loss, optimize the runner layout to shorten the filling path, and increase the metal flow rate.
Misrun
Cause: The aluminum liquid fails to fill the entire cavity, which is common in castings with large wall thickness changes, long filling distances, or insufficient temperatures.
Solution: Ensure that the metal liquid temperature is sufficient and improve the filling efficiency of the pouring system, such as thickening the main runner, increasing pressure, or using an inclined pouring method.
Crack
Cause: The casting cracks due to excessive internal stress during cooling or demolding, which can be divided into hot cracks and cold cracks.
Hot cracks usually occur when the casting is not fully solidified at high temperatures, and cold cracks occur after complete cooling.
Solution: Adjust the cooling speed to avoid too fast cooling, optimize the structure to avoid sharp corners or sudden changes in thickness, and strengthen the mold design to balance the stress distribution.
Deformation
Cause: Due to uneven cooling or unreasonable structural design, the castings are bent, warped, or out of size, especially in thin-walled or asymmetric structures.
Solution: Optimize the mold cooling system to achieve uniform cooling, avoid unilateral thickening or free cantilever structure in structural design, and use correction or heat treatment when necessary.
Sand Hole
Cause: Mainly seen in sand casting, caused by loose sand, poor exhaust, or sand falling off, forming small holes or pits on the surface of the casting.
Solution: Improve the strength of the sand, strictly control the dryness of the sand, use appropriate coatings to seal the sand surface, and improve the design of the exhaust channel to reduce pouring scouring.
Soldering (Die Sticking)
Cause: When the aluminum liquid contacts the mold, it adheres, resulting in difficulty in demolding or a rough casting surface, which is often related to improper mold temperature control and improper use of mold release agent.
Solution: Reasonably control the mold temperature to ensure uniform heating of the mold surface; use an efficient mold release agent and clean the mold cavity surface regularly.
Post-Processing Methods
Sandblasting
It is used to remove surface oxide layer, burrs and residues, provide better adhesion for subsequent coatings, and improve surface appearance.
Tumbling
It removes burrs and smooth edges through vibration friction, which is suitable for preliminary surface treatment of small and medium-sized parts.
Heat Treatment
Processes such as T5 and T6 can improve hardness, strength, and ductility, and are suitable for high-demand applications such as structural parts and bearing parts.
CNC Machining
High-precision dimensions, hole alignment, and flatness are achieved through CNC machining. Common operations include milling, drilling, boring, and tapping.
Surface Treatment Methods
Powder Coating
Provides a corrosion-resistant, beautiful, and UV-resistant protective layer in a variety of colors, suitable for outdoor or consumer products.
Painting
Covering the surface of aluminum castings with liquid paint can achieve a variety of colors and gloss effects.
Painting costs are low and are suitable for applications that require appearance but do not require high wear resistance.
Electroplating
Metal layers such as nickel or chrome plating enhance corrosion resistance, conductivity, and aesthetics, suitable for functional and decorative parts.
Electrophoresis (E-Coating)
Forming a uniform coating on the aluminum surface through an electric field, it has strong corrosion resistance and is suitable for parts with complex shapes. It is widely used in automotive interiors.
Anodizing
Thickens the natural oxide layer, improves corrosion resistance and wear resistance, can be colored, beautiful, and practical, suitable for electronics, construction, and marine fields.
CEX Casting: Leader in Aluminum Casting
CEX Casting is a professional aluminum die casting manufacturer with 29 years of experience.
Our independently developed squeeze casting equipment and processes have successfully replaced traditional die casting and serve industries with high-performance requirements.
Advantages of Squeeze Casting
Near-Zero Porosity
Squeeze casting applies high pressure during the solidification process of the casting.
It combines a closed mold cavity with an optimized feeding system to effectively remove gas and shrinkage areas, making the casting dense and extremely low in porosity.
Superior Mechanical Properties
Due to high-pressure squeeze during solidification, the aluminum crystal particles are fine, and the internal structure is uniform.
This avoids the common looseness and inclusions in traditional casting, thereby significantly improving the mechanical properties of the casting.
Heat Treatable
There are no pores and cracks in the squeeze casting process, and the structure is dense, which can meet the requirements of conventional heat treatment processes such as T5 and T6.
This allows the casting to further improve its mechanical properties according to the use requirements.
Weldable
Due to the extremely few pores in the casting and good inclusion control, squeeze casting products are not prone to problems such as pore bursting and weld brittle cracking during welding.
High Dimensional Accuracy
The metal solidifies under pressure in the mold, avoiding shrinkage deformation and insufficient filling.
The casting can achieve high-dimensional tolerance requirements in the unprocessed state.
Excellent Thermal Conductivity
The casting has a dense structure, no oxide inclusions, and good metal continuity, which greatly improves the thermal conductivity efficiency.
It is very suitable for applications with high thermal conductivity requirements, such as new energy vehicle battery housings, radiators, LED cooling systems, etc.
To verify the above technical advantages, we conducted systematic mechanical property tests and internal porosity tests on squeeze castings.
The following are the actual test results:
AlSi9Mg-T6 Mechanical Property Tests:
A356-T6 Porosity Tests:
Conclusion
Aluminum casting is an efficient and reliable manufacturing process.
A deep understanding of each process and step can help you make wise choices to improve product quality, reduce defects, and optimize production efficiency.
As a trusted die casting company, CEX Casting provides advanced aluminum squeeze casting solutions to ensure that product strength, accuracy, and consistency meet your strict requirements.
Contact us now to start your one-stop customized aluminum casting project.