Mechanical Properties of a Structural Component Processed in High-Pressure Die Casting (HPDC) with a Non-Heat-Treated Aluminum Alloy

Ditch the Furnace: Achieving High-Performance HPDC Components with Non-Heat-Treated Aluminum Alloy

This technical summary is based on the academic paper "Mechanical Properties of a Structural Component Processed in High-Pressure Die Casting (HPDC) with a Non-Heat-Treated Aluminum Alloy" by David Servando Cantú-Fernández, José Jaime Taha-Tijerina, Alejandro González, Pablo Guajardo Hernández, and Brian Quinn, published in Metals (2024).

Keywords

• Primary Keyword: Non-Heat-Treated Aluminum Alloy
• Secondary Keywords: High-Pressure Die Casting (HPDC), AuralTM-5, Mechanical Properties, Structural Components, Sustainable Manufacturing

Executive Summary

• The Challenge: The automotive industry requires lightweight structural components, but conventional heat treatment processes add significant cost, energy consumption, and CO2 emissions.
• The Method: An industrial research study evaluated the mechanical properties of an automotive shock tower, manufactured via HPDC using AuralTM-5, a non-heat-treated aluminum alloy, comparing water-quenched and non-quenched components over an eight-week natural aging period.
• The Key Breakthrough: The study successfully demonstrated that structural components made from AuralTM-5 achieve and exceed required mechanical specifications (yield strength > 110 MPa, UTS > 240 MPa, elongation ≥ 8%) without the need for thermal heat treatment.
• The Bottom Line: Eliminating heat treatment for structural HPDC components is not only feasible but also offers substantial savings in infrastructure and energy, while promoting more sustainable manufacturing practices.

The Challenge: Why This Research Matters for HPDC Professionals

In the relentless drive for vehicle lightweighting, aluminum alloys have become a go-to material for structural components. However, achieving the necessary mechanical performance often requires a costly and energy-intensive heat treatment process. This post-casting step creates production bottlenecks, increases capital expenditure for furnaces, and contributes to a larger carbon footprint. The challenge for the industry is clear: how can we achieve the high strength and ductility required for safety-critical structural parts while simplifying the production process, reducing costs, and meeting sustainability goals? This research directly confronts this challenge by exploring the viability of a non-heat-treated (NHT) alloy that promises robust mechanical properties straight from the die.

The Approach: Unpacking the Methodology

This industrial study was designed to validate the real-world performance of a specific NHT alloy in a production environment. The researchers focused on a complex, safety-critical automotive part to ensure the findings were relevant and actionable.

Method 1: Material and Component Selection
The study used AuralTM-5, an aluminum alloy specifically designed for HPDC applications requiring good fluidity and as-cast mechanical properties. The chosen component was an automotive shock tower, a large structural part with thin-wall sections, making it an ideal candidate to test the alloy's performance under demanding conditions.

Method 2: HPDC Processing and Controlled Variables
A 2700-ton cold chamber HPDC machine with a high-vacuum-assist system was used to manufacture the shock towers. To analyze the effect of post-casting cooling, two distinct groups of components were created:
* Group 1 (Quenched): Components were quenched in water at 25°C for three seconds immediately after extraction from the mold.
* Group 2 (Not Quenched): Components were allowed to cool naturally in ambient air.

Method 3: Mechanical Property Evaluation
Tensile test specimens were machined from eight different locations on each shock tower to assess the homogeneity of the casting. Yield strength, ultimate tensile strength (UTS), and elongation were measured according to ISO 6892-1 and ASTM-E8 standards. Tests were conducted within the first 24 hours and then weekly for eight weeks to monitor the effects of natural aging.

The Breakthrough: Key Findings & Data

The results provide compelling evidence for the use of NHT alloys in structural applications, while also offering crucial insights into process optimization.

Finding 1: Target Mechanical Properties Achieved Without Heat Treatment

Both quenched and non-quenched components successfully met and exceeded the minimum specifications for AuralTM-5 in the as-cast (F temper) condition. As shown in the study's data, the elongation, a critical measure of ductility, remained consistently high.

• Elongation: As depicted in Figure 4, both quenched and non-quenched samples consistently maintained elongation percentages well above the required 8% minimum, with average values exceeding 11%.
• Strength: The yield strength (Figure 5) and ultimate tensile strength (Figure 6) for both groups surpassed the minimums of 110 MPa and 240 MPa, respectively. The components also demonstrated a slight increase in strength over the eight-week evaluation period due to natural aging.

Finding 2: Quenching Enhances Process Stability, Not Just Material Properties

While both groups performed exceptionally well, the study revealed a key difference in consistency.

• Consistency: The quenched components demonstrated more stable and consistent mechanical properties throughout the eight-week analysis. As seen in the error bars in Figures 5 and 6, the non-quenched parts exhibited higher variation in their tensile and yield strength over time.
• Dimensional Stability: The authors observed that non-quenched parts, which were still hot and malleable, were prone to deformation during the automated trimming process. The quenched parts were more rigid, leading to cleaner trimming and better dimensional consistency.

Practical Implications for R&D and Operations

• For Process Engineers: This study suggests that while heat treatment can be eliminated, a simple water quench post-extraction is highly recommended. This step does not serve a metallurgical strengthening purpose but rather ensures dimensional stability for subsequent operations like trimming, reducing downtime and improving part quality. Controlling the metal temperature in the shot sleeve (above 650°C for AuralTM-5) is critical to ensure proper die filling and avoid fluidity-related defects.
• For Quality Control Teams: The data in Figure 5 and Figure 6 of the paper illustrates that natural aging has a positive, stabilizing effect on the yield and tensile strength of AuralTM-5. This indicates that mechanical properties will remain robust over the component's life. QC protocols can be simplified by eliminating the need to validate a complex heat treatment process.
• For Design Engineers: The findings indicate that AuralTM-5 is a suitable material for large, thin-walled structural components. The successful production of the shock tower demonstrates the alloy's capability. However, designers should be aware that the recommendation to quench may influence part handling and automation design immediately following the casting process.

Paper Details

Mechanical Properties of a Structural Component Processed in High-Pressure Die Casting (HPDC) with a Non-Heat-Treated Aluminum Alloy

1. Overview:

• Title: Mechanical Properties of a Structural Component Processed in High-Pressure Die Casting (HPDC) with a Non-Heat-Treated Aluminum Alloy
• Author: David Servando Cantú-Fernández, José Jaime Taha-Tijerina, Alejandro González, Pablo Guajardo Hernández, and Brian Quinn
• Year of publication: 2024
• Journal/academic society of publication: Metals
• Keywords: aluminum alloy; non-heat-treated; mechanical properties; high-pressure die casting; structural components

2. Abstract:

This industrial research focuses on the implementation and development of a productive process for an automotive structural component (Shock tower) manufactured by a high-pressure die casting (HPDC) process made of aluminum alloy AuralTM-5. This aluminum alloy has been considered in diverse automotive and aerospace components that do not require heat treatment due to its mechanical properties as cast material (F temper). On the other hand, AuralTM-5 has been designed for processing as HPDC because it is an alloy with good fluidity, making it ideal for large castings with thin-wall thicknesses, like safety structural components such as rails, supports, rocker panels, suspension crossmembers, and shock towers. The mechanical properties that were evaluated for the evaluated components were yield strength, ultimate tensile strength, and elongation. Eight samples were taken from different areas of each produced shock tower for evaluating and verifying the homogeneity of each casting. The samples were evaluated from the first hours after they were manufactured by casting until eight weeks after being produced. This was performed to understand the behavior of the alloy during its natural aging process. Two groups of samples were obtained. One set of components was heat-treated by a water quench process after the castings’ extraction and the other set of components was not quenched. Results demonstrated that both sets of components, quenched and not quenched, achieved the expected values for the AuralTM-5 of yield strength ≥ 110 MPa, ultimate tensile strength ≥ 240 MPa, and elongation ≥ 8%. Additionally, this is very important for industry since by not treating the structural components by quenching, there are savings in terms of infrastructure and energy consumption, together with benefits in the environmental aspect by avoiding CO2 emissions and being sustainable.

3. Introduction:

The automotive industry is continuously evolving toward the application of new materials to improve performance and processability. A significant trend is lightweighting, driven by performance, cost, and sustainability demands. Aluminum alloys are a primary choice due to their good corrosion resistance, high strength-to-weight ratio, and manufacturability. Novel casting technologies like high-pressure die casting (HPDC) have enabled the production of larger, more complex aluminum components, further reducing vehicle weight. However, most high-performance alloys require a heat treatment process to achieve desired mechanical properties, which adds cost and environmental impact. This has led to the development of non-heat-treated (NHT) aluminum alloys, such as AuralTM-5, which can achieve target mechanical properties through natural aging alone, aligning with the industry's need for cost-effective and sustainable manufacturing solutions.

4. Summary of the study:

Background of the research topic:

The research addresses the industrial need for lightweight automotive components that can be produced economically and sustainably. While HPDC is a highly productive process for aluminum parts, the necessity of heat treatment for conventional alloys limits its cost and environmental benefits. NHT alloys present a potential solution by eliminating this energy-intensive step.

Status of previous research:

The paper notes that while novel aluminum alloys are extensively studied, there are few research reports specifically on NHT aluminum alloys like AuralTM-5, which can achieve required physical and mechanical properties without heat treatment. Existing research confirms the benefits of HPDC for producing complex parts with good dimensional accuracy but also highlights challenges like gas entrapment and porosity.

Purpose of the study:

The study's purpose was to validate the mechanical properties of a structural automotive component (a shock tower) manufactured with the NHT alloy AuralTM-5 using an industrial HPDC process. The research aimed to determine if the alloy could meet performance specifications (yield strength, UTS, elongation) without thermal treatment and to understand the material's behavior during natural aging. A secondary goal was to compare the properties of components that were water-quenched immediately after casting versus those that were not.

Core study:

The core of the study involved manufacturing shock towers using AuralTM-5 in a 2700-ton HPDC machine. Two sets of components were produced: one set was water-quenched post-extraction, and the other was not. Tensile specimens were taken from multiple locations on the components and tested at regular intervals over eight weeks to evaluate yield strength, ultimate tensile strength, and elongation. The components were also analyzed for internal defects using X-ray radiography and blister tests.

5. Research Methodology

Research Design:

The research employed a comparative experimental design. Two groups of identical HPDC components (quenched and not quenched) were produced under controlled industrial conditions. Their mechanical properties were systematically measured over time to assess the effects of the quenching variable and natural aging.

Data Collection and Analysis Methods:

• Material Composition Analysis: The chemical composition of the AuralTM-5 ingot was verified using SPECTROLAB LAVM12 equipment under ASTM-E716 and ASTM-E3 standards.
• HPDC Process: A 2700-ton cold chamber machine with a vacuum-assist system was used. Key process parameters such as die temperature (175 °C), shot sleeve temperature (160 °C), and metal temperature (655 °C in sleeve, 715 °C in dosing furnace) were controlled and monitored.
• Mechanical Testing: Tensile tests were performed on a Zwick/Roell universal tension machine according to ISO 6892-1 and ASTM-E8 standards to determine yield stress, ultimate tensile strength, and elongation.
• Defect Analysis: Fracture surfaces were analyzed using a Nikon SMZ800N stereoscope. Internal integrity was verified with YXLON MG325 X-ray radiography equipment. A blister test (520 °C for 90 min) was conducted to detect trapped gas.

Research Topics and Scope:

The research focused on the mechanical performance of the AuralTM-5 alloy when used to produce a structural automotive shock tower via HPDC. The scope included:
- Validation of as-cast mechanical properties against material specifications.
- Analysis of the effect of natural aging over an eight-week period.
- Comparison of water-quenched versus non-quenched components.
- Investigation of casting defects and their relation to the process and alloy.

6. Key Results:

Key Results:

• Both quenched and non-quenched components achieved mechanical properties exceeding the AuralTM-5 specifications: yield strength > 110 MPa, ultimate tensile strength > 240 MPa, and elongation ≥ 8%.
• Over the eight-week natural aging period, both yield strength and ultimate tensile strength showed a tendency to increase slightly for both groups of samples.
• The non-quenched components exhibited greater variability in tensile and yield strength results over time compared to the quenched components, which showed more consistent performance.
• Elongation values for both sets of samples were high, averaging above 11%, indicating excellent ductility without heat treatment.
• Defect analysis revealed minor gas porosities (<10 µm) common to the HPDC process but no significant shrinkage or internal defects attributable to the alloy. Blister tests showed no signs of significant air entrapment.

Figure Name List:

• Figure 1. Model of the shock tower component.
• Figure 2. Specification of the specimens that were taken from the shock tower (units in mm).
• Figure 3. Schematic of the Shock tower component showing the position where the tensile coupons were obtained and areas for evaluations.
• Figure 4. Mechanical properties of elongation with and without quenching.
• Figure 5. Mechanical properties of yield strength with and without quenching.
• Figure 6. Mechanical properties of tensile strength with and without quenching.
• Figure 7. Examples of porosity in samples tested for mechanical properties.
• Figure 8. Shock towers were analyzed by X-ray technique, showing no porosity or internal defects.
• Figure 9. Results of blister test, none of the casting had an air trap.

7. Conclusion:

The study concludes that AuralTM-5 alloy is capable of achieving the specified mechanical properties for structural components in an as-cast state, eliminating the need for a separate heat treatment process. Natural aging was found to further enhance the yield and ultimate tensile strengths without negatively impacting the material. Although both quenched and non-quenched parts met specifications, the authors recommend a water quench treatment immediately after casting. This recommendation is not for achieving mechanical properties but for ensuring dimensional consistency and preventing deformation of the hot component during subsequent manufacturing steps, such as trimming. This practice leads to a more stable and productive process.

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Expert Q&A: Your Top Questions Answered

Q1: Why was AuralTM-5, an alloy with relatively low silicon (7.4%), chosen for a large, thin-walled HPDC part where fluidity is critical?

A1: The paper explains that AuralTM-5 is designed to achieve greater ductility in its as-cast state, and this is associated with its lower silicon content. While lower silicon can reduce melt fluidity, the researchers compensated for this by carefully managing the process temperatures. They maintained a high temperature in the dosing furnace (715 °C ± 10 °C) and ensured the metal temperature inside the shot sleeve remained above 650 °C to prevent pre-solidification and ensure complete cavity filling.

Q2: The paper recommends water quenching, but the main benefit of the alloy is that it's "non-heat-treated." Isn't that a contradiction?

A2: This is a key distinction. The water quench recommended in the study is not a metallurgical heat treatment (like a T5 or T6 temper) intended to alter the microstructure for strength. Instead, it serves a purely mechanical purpose. The rapid cooling makes the hot, freshly cast part more rigid, preventing it from deforming during handling by the extraction robot and during the subsequent high-force trimming operation. The mechanical properties are achieved with or without this quench, but the quench ensures better process stability and dimensional accuracy.

Q3: What was the primary type of defect observed, and was it related to the AuralTM-5 alloy itself?

A3: The main defect found was small gas porosities, below 10 µm in diameter. The paper states that these porosities were not related to the AuralTM-5 alloy chemistry but are commonly formed during the first stage of the HPDC injection process due to air entrapment. Importantly, X-ray and blister tests confirmed the absence of significant internal defects like shrinkage, indicating the alloy and process parameters were well-matched.

Q4: How significant is the effect of natural aging on the alloy's properties?

A4: The study showed that natural aging over eight weeks has a positive and stabilizing effect. Both yield strength and ultimate tensile strength demonstrated a slight but consistent increase over this period for both quenched and non-quenched parts. This indicates that the components will maintain or even slightly improve their strength characteristics over time, providing confidence in their long-term performance without any artificial aging processes.

Q5: What is the single most critical process parameter to control when working with this alloy?

A5: Based on the authors' observations, the most critical parameter was the metal temperature inside the shot sleeve. Early attempts with metal below the liquidus point resulted in incomplete filling of the die cavity. The study strongly recommends maintaining a temperature above 650 °C for AuralTM-5 in the shot sleeve to prevent pre-solidifying, ensure proper fluidity, and achieve a completely filled, defect-free component.

Conclusion: Paving the Way for Higher Quality and Productivity

This research provides a clear and data-backed pathway for producing high-performance structural components while significantly reducing manufacturing complexity and cost. By demonstrating the robust capabilities of a Non-Heat-Treated Aluminum Alloy like AuralTM-5, the study proves that the costly, energy-intensive furnace can be eliminated from the production line without sacrificing mechanical integrity. The key takeaway is that excellence in as-cast properties is achievable, and simple process adjustments, like a post-extraction quench, can ensure the dimensional stability needed for high-volume, automated production.

At CASTMAN, we are committed to applying the latest industry research to help our customers achieve higher productivity and quality. If the challenges discussed in this paper align with your operational goals, contact our engineering team to explore how these principles can be implemented in your components.

Copyright Information

This content is a summary and analysis based on the paper "Mechanical Properties of a Structural Component Processed in High-Pressure Die Casting (HPDC) with a Non-Heat-Treated Aluminum Alloy" by "David Servando Cantú-Fernández, et al.".

Source: https://doi.org/10.3390/met14030369

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