Analysis and Evaluation of Effect of Manganese Content on Properties of EN AC 46000 Aluminum Alloy

The Manganese Solution: How a Small Alloy Addition Transforms EN AC 46000 HPDC Properties

This technical summary is based on the academic paper "Analysis and Evaluation of Effect of Manganese Content on Properties of EN AC 46000 Aluminum Alloy" by Martyna Pasternak, Marcin Brzeziński, and Gabriela Piwowarczyk, published in the Journal of Casting & Materials Engineering (2019). It has been analyzed and summarized for technical experts by CASTMAN.

Keywords

• Primary Keyword: Manganese in Aluminum Alloys
• Secondary Keywords: EN AC 46000, HPDC, aluminum die casting, mechanical properties, iron correction

Executive Summary

• The Challenge: High iron content in die-cast Al-Si alloys, necessary to protect tooling, creates brittle phases that degrade mechanical properties and cause defects.
• The Method: Researchers in an industrial foundry systematically increased the manganese content in an EN AC 46000 aluminum alloy from 0.29% to 0.47%.
• The Key Breakthrough: The increased manganese content significantly improved strength properties, refined the microstructure by altering harmful iron phases, and improved casting soundness by lowering the density index.
• The Bottom Line: Intentionally increasing manganese is a cost-effective strategy to neutralize the negative effects of iron, leading to higher quality, greater tightness, and fewer defects in HPDC components.

The Challenge: Why This Research Matters for HPDC Professionals

In high-pressure die casting (HPDC), a certain level of iron in aluminum alloys is often recommended to reduce the molten metal's impact on the pressure chamber and mold. However, this necessary iron content comes with a significant drawback. Iron precipitates in the form of very brittle, needle-like Al4Si2Fe compound crystals. These phases act as stress risers, causing a decrease in mechanical properties, especially plasticity and impact strength. For engineers in the automotive industry and other high-performance sectors, this can lead to component failures, leaks, and cracks—costly problems that compromise quality and reliability. The central challenge is how to retain the tooling-protection benefits of iron while mitigating its disastrous effect on the final casting's integrity.

The Approach: Unpacking the Methodology

This study was conducted under real-world industrial conditions at a Polish foundry specializing in aluminum alloys. The research focused on the widely used EN AC 46000 (also designated AK 93 or AlSi9Cu3(Fe)) alloy.

The core of the methodology was a gradual increase of the manganese content in the melt. Starting with an initial concentration of 0.29% Mn, the researchers added alloy pigs with a higher manganese content to the furnace, progressively raising the concentration to a final level of 0.471%. This gradual approach was necessary to maintain process continuity in a production environment.

To evaluate the effects of this change, the team conducted a series of rigorous tests on samples taken throughout the process:
* Chemical Composition: Analyzed using a SpectroMAXx spectrometer.
* Tensile Strength: Tested in accordance with the ISO 6892-1 standard.
* Density Index: Measured using an MK 300 Electronic Density Index Balance to evaluate material soundness and porosity.
* Porosity: Examined using X-ray scanning to identify internal defects.

Samples were evaluated both before and after a standard argon refining (barbotage) process to provide a comprehensive picture of the material's properties.

The Breakthrough: Key Findings & Data

The research yielded clear, quantifiable improvements across several key performance indicators, demonstrating the powerful effect of optimizing the manganese content.

Finding 1: Significant Enhancement of Mechanical Strength

The addition of manganese directly translated to superior strength properties. The data shows a clear advantage for the alloy with increased manganese content, particularly in yield strength, which is critical for component performance under load.

As shown in Table 2, the yield strength (Rp) of the alloy after refining saw a substantial increase. The standard alloy achieved a yield strength of 214.8 MPa, whereas the alloy with increased manganese reached 244.5 MPa, an improvement of nearly 14%. Similarly, the tensile strength (Rm) of the high-manganese alloy before refining was 222 MPa, significantly higher than the standard alloy's 176 MPa.

Finding 2: Improved Material Soundness and Microstructure

Manganese proved highly effective at improving the internal quality of the castings. This was confirmed by two key metrics: density index and microstructural analysis.

• Density Index: A lower density index indicates less gas and shrinkage porosity, resulting in a sounder casting. As detailed in Table 3, the density index of the high-manganese alloy after refining was 0.54%, a marked improvement over the standard alloy's 0.64%.
• Microstructure: The visual evidence is compelling. Figure 4 shows the microstructure of the initial alloy (0.29% Mn), where porosity is visible. In contrast, Figure 5, showing the alloy with increased Mn content (0.47%), reveals a more refined and compact microstructure. This is the direct result of manganese transforming the harmful, needle-like iron phases into small, compact polygonal crystals that are less detrimental to the alloy's integrity.

Practical Implications for R&D and Operations

The findings from this study offer actionable insights for improving quality and efficiency in HPDC operations.

• For Process Engineers: This study suggests that carefully managing and adjusting the manganese-to-iron ratio in the melt is a powerful tool for neutralizing iron's harmful effects. This can lead to a more stable production process with a lower rate of defects like cracks and leaks.
• For Quality Control Teams: The data in Table 2 (Strength values) and Table 3 (Density index values) of the paper illustrates the direct correlation between higher manganese content, improved mechanical properties, and greater casting soundness. This could inform new, more stringent quality inspection criteria for high-integrity components.
• For Design Engineers: The findings indicate that for components with complex geometries or those susceptible to leakage under pressure, specifying an alloy with an optimized manganese content can proactively mitigate the risk of failure caused by iron-phase embrittlement, leading to more robust and reliable designs.

Paper Details

Analysis and Evaluation of Effect of Manganese Content on Properties of EN AC 46000 Aluminum Alloy

1. Overview:

• Title: Analysis and Evaluation of Effect of Manganese Content on Properties of EN AC 46000 Aluminum Alloy
• Author: Martyna Pasternak, Marcin Brzeziński, Gabriela Piwowarczyk
• Year of publication: 2019
• Journal/academic society of publication: Journal of Casting & Materials Engineering
• Keywords: aluminum alloy, pressure casting, manganese, strength of material

2. Abstract:

This article is the effect of industrial work and many surveys in the one of the Polish foundries that specialize in aluminum alloys. The main goal of our explorations is to evaluate the influence of manganese on Al-Si alloy properties. In die-cast alloys, it is recommended to use larger amounts of iron to reduce the impact on the pressure chamber and mold. Manganese neutralizes the harmful effect of iron by changing the morphology of the separated brittle ferrous phases. The unfavorable form of the iron-containing phases in the form of long needles changes into the forms of fine compact crystals, which are less harmful to the mechanical properties. Nowadays, the main client requirement is to obtain the right parameters at the best price. Specifically, the customer is in the automotive industry, where new technologies provide a connection between the high quality and low weight of car parts [1-3].

3. Introduction:

The introduction of a completely new alloy often involves changes in the casting process, purchases of new machinery (or the modernization of the existing devices), training employees, and changes in occupational health and safety conditions. Not only do the casting parameters change, but they are also sometimes further processed. Attention should also be paid to the ratio of the price of alloying elements to the properties obtained by their use. These aspects lead to the correction of existing processes, where sometimes a small change can have great beneficial effects. The impact of alloying elements are as follows.
• Copper - increases tensile strength and hardness as well as improves machinability and resistance to heat loads. At the same time, it reduces elongation and deteriorates corrosion resistance. The change of properties is caused by the strengthening of the a(Al) phase.
• Zinc - similar effects as with copper, but its content within a range of 0.05-2% classifies it as an impurity, while it is treated as an alloying element above 5%.
• Magnesium - in liquid metal, it combines with silicon to form Mg2Si compounds. These compounds are characterized by variable solubility in the solid solution a(Al), which allows the use of heat treatment in castings made of AlSi alloys. This increases the properties of castings such as their hardness, tensile strengths and yield strengths.
• Nickel - has a stronger effect than copper; its effect is noticeable in the case of changes in the mechanical properties of castings operating at elevated temperatures by preventing their deterioration.
• Silicon - the basic component of silumins; it has a significant influence on their casting properties. The best results are obtained with the composition of silumins close to eutectic. An increase in its compactness is connected with a decrease in the value of the thermal expansion coefficient of silumens, which is very important in the case of castings operating at elevated temperatures with high requirements for dimensional stability.
• Iron, tin, lead, and zinc are the main impurities of AlSi alloys, and (as mentioned earlier) Zn can be treated as an alloying element in relevant alloying contents.
• Iron in alloys occurs in the form of coniferous crystals of a very brittle Al4Si2Fe compound causing a decrease in mechanical properties, especially the plastic properties and impact strength of castings. The addition of 0.3-0.45% Mn transforms the inclusions of the phase that contains iron into the form of small compact polygonal crystals, which no longer have a negative effect on the strength properties. In die-cast alloys, it is recommended to use larger amounts of iron in order to reduce the effect on the pressure chamber and mold. Higher iron contents therefore require the use of larger amounts of manganese.

4. Summary of the study:

Background of the research topic:

In Al-Si die casting alloys, iron is often used to protect equipment, but it forms brittle, needle-like phases that harm mechanical properties. Manganese is known to counteract this effect by altering the morphology of these iron-containing phases into a less detrimental, more compact form.

Status of previous research:

The paper builds on the established understanding of how various alloying elements (Cu, Zn, Mg, Ni, Si, Fe) affect the properties of Al-Si alloys. Specifically, it focuses on the known principle that adding 0.3-0.45% Mn can transform harmful iron-containing phases.

Purpose of the study:

The main goal was to evaluate the influence of increased manganese content on the properties of EN AC 46000 Al-Si alloy within an industrial production environment, aiming to improve casting quality and reduce defects like leaks and cracks.

Core study:

The study involved gradually increasing the manganese content in an EN AC 46000 alloy from an initial 0.29% to a final 0.471% in a production furnace. The effects of this change on mechanical strength, density index, microstructure, and porosity were systematically measured and analyzed.

5. Research Methodology

Research Design:

The study was an industrial experiment conducted in a pressure foundry. It involved a progressive modification of the alloy's chemical composition and a comparative analysis of material properties before and after the change.

Data Collection and Analysis Methods:

Data was collected through spectrometric analysis for chemical composition, tensile testing according to ISO 6892-1, density index measurement using an electronic balance, and porosity detection via X-ray scanning. Samples were tested both before and after argon refining.

Research Topics and Scope:

The research was scoped to the EN AC 46000 (AlSi9Cu3(Fe)) alloy used in a high-pressure die casting process. The primary variable was the manganese content, and the evaluated properties included tensile strength, yield strength, density index, and microstructure.

6. Key Results:

Key Results:

• Increasing manganese content improves the strength properties of castings (Table 2).
• The alloy with increased manganese showed improved microstructures, with harmful iron phases transformed into less detrimental forms (Fig. 5).
• The density index values improved (decreased) with higher manganese content, indicating better material soundness (Table 3).
• The changes led to increased tightness and stabilized the overall quality of the castings.

Figure Name List:

• Fig. 1. Shrinkage porosity- microstructural image according to [4]
• Fig. 2. Course of Mn content growth in subsequent tests of chemical composition
• Fig. 3. Dimensions of sample for strength test [6, 7]
• Fig. 4. Microstructure of casting made of alloy with initial Mn content (0.29%)
• Fig. 5. Microstructure of casting made of alloy with increased Mn content (0.47%)
• Fig. 6. Fragment of X-ray image

7. Conclusion:

The obtained results indicated the correctness of our initial hypotheses. It has been discovered that the increase content of manganese affects the following:
• improves strength properties of castings (Tab. 2);
• improves casting microstructures;
• improves density index values (Tab. 3);
• increases tightness of castings;
• stabilizes quality of castings.
The proposed change in production is related only to the input introduced into the melting furnace. The purchase of alloys with increased manganese contents is connected with slightly higher costs, which will be compensated by reducing the shortages.

8. References:

• [1] Poniewierski Z. (1989). Krystalizacja, struktura i właściwości siluminów. Warszawa: Wydawnictwo Naukowo-Techniczne.
• [2] Poniewierski Z. (1966). Modyfikacja siluminów. Warszawa: Wydawnictwo Naukowo-Techniczne.
• [3] Górny Z., Sobczak J. (2005). Nowoczesne tworzywa odlewnicze na bazie metali nieżelaznych. Kraków: ZA-PIS.
• [4] BDG standard - P202 "Volume Deficits of Casting Made from Aluminium, Magnesium, and Zinc Casting Alloys"
• [5] EN AC-46000 AC-AlSi9CU3(FE) (2010)
• [6] ISO 6892-1; First edition 2009-08-15
• [7] PN-EN ISO 6892-1

Expert Q&A: Your Top Questions Answered

Q1: Why was a gradual increase in manganese content used instead of creating entirely new, separate batches for comparison?

A1: The paper states this approach was dictated by the realities of an industrial production environment. The researchers noted the "necessity of maintaining process continuity," as it was not possible to completely empty the furnace to load a new batch. This method allowed them to conduct the experiment without disrupting the foundry's ongoing operations.

Q2: The paper mentions that iron is recommended in die-cast alloys. Why deliberately use an element that is known to be harmful to mechanical properties?

A2: According to the abstract and introduction, larger amounts of iron are intentionally used in die-cast alloys to "reduce the impact on the pressure chamber and mold." This practice, often called preventing "die soldering," protects expensive tooling. The addition of manganese is the corrective action taken to neutralize the negative structural effects of this necessary iron content.

Q3: How exactly does manganese neutralize the harmful effect of iron in the alloy?

A3: The paper explains that manganese works by "changing the morphology of the separated brittle ferrous phases." The unfavorable form of these phases, which are long, sharp needles, are transformed by manganese into "fine compact crystals" or "small compact polygonal crystals." These rounded, more compact shapes are less harmful to the alloy matrix and do not act as significant stress concentrators.

Q4: Did the increase in manganese completely eliminate porosity in the castings?

A4: No, it did not lead to complete elimination. The X-ray image in Figure 6 shows that even in the improved alloy, "small porosities are acceptable." The paper notes that "in pressure castings, there are always small porosities associated with the specification of this type of casting." The goal was to reduce porosity and improve soundness, which was successfully demonstrated by the improved density index values.

Q5: What was the specific effect of the argon refining process on the alloys?

A5: The data in Tables 2 and 3 shows that argon refining had a positive effect on both the standard and high-manganese alloys. For the high-manganese alloy, refining dramatically improved the density index, lowering it from 3.73% to just 0.54% (Table 3). This indicates a significant reduction in gas content and porosity, leading to a much sounder final casting.

Conclusion: Paving the Way for Higher Quality and Productivity

This research provides clear, industrial-scale evidence that addresses a fundamental challenge in HPDC: balancing tooling protection with casting integrity. The deliberate addition of iron, while necessary, introduces a significant risk of producing brittle, unreliable components. The key takeaway is that an optimized level of Manganese in Aluminum Alloys is not just a minor tweak but a powerful metallurgical tool.

By increasing the manganese content in EN AC 46000, the foundry was able to transform harmful iron phases, resulting in demonstrably higher strength, improved microstructure, and greater casting soundness. This is a practical, cost-effective strategy that directly translates to reduced scrap rates, higher component reliability, and more stable production quality.

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 "Analysis and Evaluation of Effect of Manganese Content on Properties of EN AC 46000 Aluminum Alloy" by "Martyna Pasternak, Marcin Brzeziński, Gabriela Piwowarczyk".
• Source: http://dx.doi.org/10.7494/jcme.2019.3.1.14

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