The mechanical properties of aluminum die castings are determined by alloy composition, processing characteristics, and microstructure. In industrial production, the as-cast properties of mainstream die-cast aluminum alloys fall within a specific range: tensile strength of 250-310 MPa, yield strength of 130-165 MPa, and elongation of 1.5%-3%. This performance level is influenced by the ratio of alloying elements such as silicon and copper, as well as by porosity and microstructure.
This article will begin with performance benchmark data, further analyze the mechanism of alloying elements, examine the constraints of porosity and microdefects, and ultimately explore the performance boundaries of existing processes to help you establish a comprehensive understanding.
The Typical Mechanical Property Ranges of Aluminum Die Castings
Interpretation of Core Performance Parameters
Tensile strength, yield strength, elongation, and hardness together constitute the core indicators for evaluating the mechanical properties of aluminum die castings:
- Tensile Strength: This is the material’s ability to resist maximum tensile load and determines the component’s load-bearing limit.
- Yield Strength: This is the critical point at which a material begins to undergo significant plastic deformation and is the primary basis for structural component design.
- Elongation: This reflects the material’s plastic deformation capacity and directly affects the component’s impact resistance and safety.
- Hardness: This reflects the material’s ability to resist localized indentation or scratching and is closely related to wear resistance.
Performance Benchmarks for Common Die-Cast Aluminum Alloys
The data in the following table represents the as-cast performance range that can be reliably achieved for aluminum die casting parts under normal, stable industrial production conditions.
This data fully accounts for the impact of common defects such as porosity and serves as a practical benchmark for engineering design:
|
Alloy Grade |
Standard System | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) | Brinell Hardness (HB) |
| A380 | AA | 200-250 | 110-130 | 1.5-3.0 |
75-85 |
|
ADC12 |
JIS | 190-240 | 100-130 | 1.0-3.0 | 80-95 |
| A360 | AA | 210-260 | 120-140 | 2.0-4.0 |
70-80 |
|
A383 |
AA | 200-250 | 110-130 | 2.0-4.0 | 70-80 |
| A413 | AA | 190-240 | 100-120 | 2.0-3.5 |
75-85 |
|
B390 |
AA | 240-290 | 200-230 | <0.5 | 110-120 |
| 518 | AA | 150-190 | 90-110 | 5.0-10.0 |
55-65 |
|
AlSi9Cu3 |
EN | 190-240 | 100-130 | <1.5 | 85-95 |
| AlSi10Mg | EN | 190-240 | 100-130 | 1.0-2.0 |
80-90 |
|
AlSi12(Cu) |
EN | 200-250 | 110-140 | <1.0 |
85-95 |
Die-Cast Aluminum Alloy As-Cast Mechanical Properties (Industrial Production Practice Benchmark)
It’s important to emphasize that a performance “range” is more valuable for engineering reference than a single ideal value.
The table clearly illustrates the positioning of different alloys:
A380/ADC12 offers the best balance of all aspects and is the preferred general-purpose choice, B390 offers ultra-high wear resistance but the lowest toughness, and 518 alloy sacrifices strength for excellent toughness and corrosion resistance.
How Alloy Composition and Microstructure Determine Performance Benchmarks
The Core Role of Silicon (Si)
Improving Flowability
Silicon plays a crucial role in die-cast aluminum alloys. It significantly improves the flowability of the molten metal while lowering the solidification temperature range.
This property enables the molten aluminum to perfectly fill thin-walled areas and complex structures, providing the foundation for achieving complete castings.
Excellent flowability directly affects the molding quality and dimensional accuracy of the product. The following diagram illustrates the relationship between silicon content and fluidity:
Silicon Content Aluminum Fluidity Diagram
Improving Strength and Hardness
In terms of strengthening mechanisms, silicon effectively improves the material’s strength and hardness by dissolving in the aluminum matrix and forming fine silicon phase particles.
This strengthening effect enables castings to withstand higher mechanical loads and meet the strength requirements of various applications.
Proper control of silicon content is crucial for achieving desired mechanical properties.
Inherent “Source of Brittleness”
However, silicon acts like a double-edged sword.
When the silicon content exceeds the eutectic point (11.7%), especially when coarse, plate-like hypereutectic silicon phases form, these hard and brittle phases can severely fracture the aluminum matrix, acting as stress concentration points.
This microstructural change directly leads to a sharp decrease in the material’s toughness (elongation), a necessary performance trade-off when pursuing high fluidity.
The Trade-off Between Copper (Cu) and Magnesium (Mg)
The Strengthening Mechanisms and Costs of Copper
Copper plays a crucial role in die-cast aluminum alloys through solid solution strengthening, significantly improving the material’s strength, hardness, and high-temperature performance.
This strengthening effect makes copper-containing alloys particularly suitable for structural parts requiring high mechanical properties and applications with high operating temperatures.
However, this performance improvement comes at the expense of corrosion resistance. Increased copper content directly impairs the density and self-healing ability of the aluminum surface oxide film.
The Unique Advantages of Magnesium
Magnesium exhibits unique performance characteristics in aluminum alloys. It moderately increases material strength while effectively maintaining the alloy’s excellent ductility.
This characteristic makes magnesium-containing alloys excellent in applications requiring a certain degree of toughness.
More importantly, magnesium is a key factor in achieving the alloy’s excellent corrosion resistance and ideal anodizing results, directly impacting the material’s surface finish quality and long-term performance.
The Double-Edged Sword Effect of Iron (Fe)
Essential for Anti-Sticking Molds
In die-cast aluminum alloys, iron forms a stable Al-Fe intermetallic compound, creating an effective physical barrier between the molten aluminum and the die steel surface.
This property fundamentally prevents welding between the molten aluminum and the die surface and is a key technical measure for the smooth operation of the high-pressure die casting process.
Without an appropriate amount of iron, industrialized aluminum die casting would be difficult to achieve.
The “Killer” of Toughness
The hard, brittle, needle-like β-Al5FeSi phase formed by iron and aluminum severely disrupts the continuity of the aluminum matrix during solidification.
These needle-like compounds act as stress concentration points when the material is subjected to stress, preferentially initiating microcracks and providing pathways for their propagation.
This microstructural characteristic directly leads to a significant decrease in the material’s toughness and is the core underlying reason for the generally low elongation of aluminum die castings.
The figure below illustrates the microstructure of the needle-like β-Al5FeSi phase:
β-Al5FeSi Needle Phase Microstructure
The Constraint of Defects on Mechanical Performance
Porosity: The Main Limiting Factor of Performance
The Formation Mechanism of Porosity
Porosity defects primarily arise from two key processes: First, during high-speed filling, gases entrained in the molten metal are unable to escape the mold cavity due to flow resistance, forming air porosity.
Second, during the solidification shrinkage phase, localized shrinkage porosity is caused by inadequately designed feeding systems or improper process parameters.
These two formation mechanisms together constitute the primary sources of porosity defects.
For more information on the causes and types of porosity in aluminum die castings, click here to learn more. The figure below illustrates two common types of porosity:
Gas Porosity & Shrinkage Porosity
The Damage Mechanism of Porosity
The impact of pores on casting performance is primarily due to their role as stress concentration points.
These microscopic defects significantly reduce the effective load-bearing cross-sectional area of aluminum die castings and induce stress concentration under load, severely compromising the material’s tensile strength, elongation, and fatigue life.
The presence of pores, particularly in thin-walled areas and critical stress-bearing locations, can directly weaken the structural integrity of the part.
Dynamic Impact of Porosity
Under alternating loads, pore edges are highly susceptible to fatigue crack initiation. These microcracks continue to propagate under cyclic stress, ultimately leading to premature failure of the part.
Even under static loading, pores significantly reduce the material’s fracture toughness and increase the risk of brittle fracture.
Microstructural Defects: The Intrinsic Cause of the Performance Boundaries
Structural Barriers of Brittle Phases
At the microscopic level, established hard and brittle phases (such as Al5FeSi) create “structural barriers” that cannot be eliminated through subsequent processing.
These brittle phases preferentially crack when subjected to stress, maintaining the material’s toughness at a low level.
This means that even with optimized aluminum die casting processes, the material’s elongation is still limited by the presence of these inherently brittle phases.
Inherent Limitations of Alloy Design
The design of a specific alloy composition is essentially a balancing act between properties.
For example, the design of B390, which achieves exceptional wear resistance through a high silicon content, inherently determines its extremely low elongation from the moment its composition is determined.
This performance characteristic is a direct result of the material’s composition design and is inherent in the material.
Performance Boundaries within the Existing Die Casting Process Framework
The Limits of Conventional Die Casting Processes
Optimizing injection parameters and mold temperature can improve the flow and solidification of the molten metal, leading to limited improvements in material density.
However, due to the inherent high-speed filling nature of conventional die casting, porosity and shrinkage defects cannot be eradicated.
This reality results in an inherent baseline for the mechanical properties of aluminum die casting parts, and a clear upper limit to the optimization potential of conventional processes.
Technical Limits of Heat Treatment Processes
Traditional Aluminum Die Casting
The heat treatment capabilities of traditional aluminum die castings are limited by internal porosity defects, making them unable to withstand the T6 solution treatment process.
During the high-temperature solution treatment, trapped gas in the pores expands, causing blistering and dimensional deformation on the casting surface.
Therefore, conventional die casting often uses T5 low-temperature aging as an alternative.
This treatment, performed in the 150-200°C temperature range, achieves stress relief and structural stabilization.
However, due to the lack of solution strengthening, the performance improvement is limited.
Squeeze Casting
In contrast, the squeeze casting process, thanks to its unique forming mechanism, inherently offers higher material density, fully utilizing the benefits of the T6 heat treatment.
The synergistic effects of solution strengthening and aging strengthen the casting, resulting in superior overall mechanical properties.
To learn more about how the squeeze casting process achieves high-performance castings, please click here.
The image below shows a real-world shot of CEX Casting performing T6 heat treatment on squeeze casting parts:
Squeeze Casting T6 Heat Treatment at CEX Casting
Conclusion
The mechanical properties of aluminum die casting parts are essentially the result of a precise balance between alloy composition, die casting process characteristics, and microstructure.
A correct understanding of their strength and toughness levels does not negate technical capabilities, but rather demonstrates a deep understanding and respect for the laws of materials science.
As a leading aluminum die casting manufacturer in China, CEX Casting not only masters the intricacies of traditional die casting technology but also possesses expertise in advanced casting technologies such as squeeze casting.
We deeply understand the characteristics and boundaries of different process routes and can provide comprehensive and professional advice to clients, from material selection to process solutions, tailored to specific project needs.
Please feel free to contact us to provide you with the most cost-effective aluminum die casting solutions.