Application of Aluminum Alloy Semi-Solid Processing Technology in Automobile: A Review

This article introduces the paper ['Application of Aluminum Alloy Semi-Solid Processing Technology in Automobile: A Review'] published by ['International Journal of Automotive Manufacturing and Materials'].

1. Overview:

  • Title: Application of Aluminum Alloy Semi-Solid Processing Technology in Automobile: A Review
  • Author: Hongxing Lu, Zhengbai Liu, and Qiang Zhu
  • Publication Year: 2023
  • Publishing Journal/Academic Society: International Journal of Automotive Manufacturing and Materials
  • Keywords: semi-solid processing technology; aluminum alloy; application; automobile

2. Abstracts or Introduction

Abstract:
"Semi-solid processing technology is a new forming technology for aluminum alloy components, which has advantages in producing high-quality components with complex shapes. Several methods of semi-solid metal preparing and forming have been developed in the past 50 years. Some methods have been applied to provide high-quality components or improve castings' quality in the field of automobile. This paper reviews the development and application of semi-solid processing technology and discusses about its future application prospects."

Introduction:
"In recent years, automobile manufacturers, especially new energy automobile manufacturers, have paid more and more attention to automobile light weighting as it is beneficial to saving energy, reducing exhaust emissions, and lowering comprehensive manufacturing cost. Replacing iron and steel components with aluminum alloy components can significantly reduce the body weight of a vehicle because the density of aluminum alloy is only about 1/3 of that of iron or steel. However, a challenge for increasing the aluminum consumption in automobiles is that both of the strength and elastic modulus of aluminum alloy are usually lower than those of iron and steel, which leads to a higher quality requirement on aluminum alloy components than iron and steel components.
The aluminum alloy components are usually fabricated by plastic deformation processes (e. g., rolling, extruding, punching, and forging) or casting processes (e.g., sand casting, permanent mold casting, lost foam casting, and high pressure die casting). The plastic-formed components have good quality and performance, and can be used under high stress conditions. However, the plastic forming processes cannot be used to produce components with complex shapes. Although the casting processes can be used to produce components with complex shapes, the quality and performance of cast components are usually lower than those of plastic formed components due to the occurrence of casting defects. Therefore, developing and producing high-quality and complex-shaped aluminum alloy components is still a big challenge for automobile components suppliers.
Semi-solid processing technology is a new forming technology for aluminum alloy components, which originated from Massachusetts Institute of Technology in 1970s [1,2]. In this process, alloys are prepared into solid-liquid mixed state which is called semi-solid metal. In semi-solid metal, solid particles, which are spherical or nearly spherical, suspend in liquid metal. Compared with liquid metal, semi-solid metal has special rheological property, flow behavior and solidification behavior [3,4]. Under shear stress, semi-solid metal can flow like liquid and the fluid viscosity of semi-solid metal decreases as the shear stress increases."

3. Research Background:

Background of the Research Topic:

The automotive industry is increasingly focused on vehicle lightweighting to achieve energy efficiency, reduce exhaust emissions, and lower manufacturing costs. Substituting ferrous components with aluminum alloys is a significant strategy for weight reduction due to aluminum's density being approximately one-third that of iron or steel. However, the lower strength and elastic modulus of aluminum alloys compared to iron and steel necessitate higher quality standards for aluminum alloy components in automotive applications.

Status of Existing Research:

Conventional manufacturing routes for aluminum alloy components include plastic deformation processes (e.g., rolling, extrusion, forging) and casting processes (e.g., sand casting, permanent mold casting, high pressure die casting (HPDC)). Plastic deformation yields components with superior quality and performance suitable for high-stress applications, but it is limited in producing complex geometries. Casting processes offer greater design freedom for complex shapes, but typically result in lower quality components due to inherent casting defects compared to plastic formed counterparts. Therefore, the production of high-quality, complex-shaped aluminum alloy components remains a significant challenge for automotive suppliers.

Necessity of the Research:

To address the limitations of traditional manufacturing methods, semi-solid processing technology has emerged as a novel forming technique for aluminum alloys. Originating from research at MIT in the 1970s [1,2], this technology utilizes a solid-liquid mixed state of metal, termed semi-solid metal, where spherical or near-spherical solid particles are suspended in a liquid matrix. Semi-solid metal exhibits unique rheological properties, flow behavior, and solidification characteristics [3,4]. Notably, under shear stress, it behaves like a liquid with viscosity decreasing as shear stress increases. This characteristic allows for the forming of complex shapes with improved quality compared to traditional casting and approaching that of plastic formed components. Consequently, semi-solid processing technology has been adopted to produce high-integrity castings and enhance casting quality in various sectors, including automotive, motorcycle, bicycle, and telecommunications [5-7].

4. Research Purpose and Research Questions:

Research Purpose:

This review paper aims to comprehensively examine the advancements and applications of semi-solid processing technology for aluminum alloys, specifically within the automotive sector. It further explores the future potential and prospects of this technology.

Key Research:

The key research areas investigated in this paper include:

  • Development and classification of semi-solid metal preparation techniques, encompassing both thixo-route (partial melting of solid metal) and rheo-route (partial solidification of liquid metal) methods.
  • Overview of semi-solid metal forming processes, including forging, extrusion, HPDC, and emerging techniques like additive manufacturing.
  • Analysis of the application of semi-solid processing in automotive manufacturing, focusing on producing high-quality components and improving the quality of castings.

Research Hypotheses:

While not explicitly stated as formal hypotheses, the paper implicitly investigates the premise that semi-solid processing technology offers a viable and advantageous alternative for manufacturing high-quality, complex aluminum alloy components in the automotive industry, addressing the limitations of conventional casting and plastic deformation methods. It also explores the hypothesis that rheo-HPDC is becoming the mainstream process in semi-solid processing for automotive applications.

5. Research Methodology

Research Design:

This study employs a review-based research design, synthesizing existing literature and industrial applications to provide a comprehensive overview of aluminum alloy semi-solid processing technology in the automotive industry.

Data Collection Method:

The data collection method involves a thorough review of published research articles, technical reports, and industrial case studies related to semi-solid processing of aluminum alloys. The literature search encompasses scientific databases and industry publications to gather information on process development, applications, and performance characteristics.

Analysis Method:

The analysis method is qualitative, focusing on summarizing and synthesizing the collected data to:

  • Classify and describe different semi-solid metal preparation and forming techniques.
  • Analyze the advantages and limitations of semi-solid processing compared to conventional methods.
  • Evaluate the current applications and future trends of semi-solid processing in automotive manufacturing.
  • Identify key research results and practical implications based on reviewed literature.

Research Subjects and Scope:

The research subjects are aluminum alloy semi-solid processing technologies, encompassing both material preparation and component forming methods. The scope is specifically focused on the application of these technologies within the automotive industry, considering aspects such as component quality, manufacturing efficiency, and future application prospects.

6. Main Research Results:

Key Research Results:

The review highlights the two primary routes for semi-solid metal preparation: thixo-route and rheo-route. The thixo-route, involving partial melting of solid metal, is further categorized into Type I, utilizing special melt solidification techniques like magneto-hydro-dynamic stirring (MHD) [8-10], spray forming (Ospray) [11,12], and cooling slope (SC) [13], and Type II, employing plastic deformation processes such as Strain-Induced Melt Activation (SIMA) [14-17], Recrystallisation and Partial Melting (RAP) [9,13,18], and Equal-Channel Angular Pressing [19]. The rheo-route, involving partial solidification of liquid metal, includes technologies like Swirled Enthalpy Equilibration Device (SEED) [20-23], Enthalpy Control Process (ECP) [24,25], Gas Induced Semi-Solid (GISS) [26-30], Rapid Slurry Formation (RSF/RheoMetal) [31-33], Cooling Slope (CS) [34-36], and Air-Cooled Stirring Rod Device (ACSR) [37-39].

Thixo-route is typically suited for solid fractions above 50%, while rheo-route is preferred for solid fractions below 50%. Rheo-route methods are generally more energy-efficient and cost-effective, making them a focal point in semi-solid metal preparation development since the early 2000s. SEED, GISS, RSF, and ACSR are notably used for producing automobile aluminum alloy components.

Semi-solid metal forming technologies have evolved significantly, encompassing forging, extruding, HPDC, sand casting, and permanent mold casting. Thixo-forging, rheo-forging, thixo-HPDC, and rheo-HPDC have achieved industrial application. Thixo-processes typically use semi-solid metal with 50-70% solid fraction (thixo-route), while rheo-processes use less than 50% solid fraction (rheo-route). HPDC offers advantages in component shape complexity and production efficiency over forging, making semi-solid HPDC particularly suitable for automotive components. Additive manufacturing of semi-solid metal is identified as a recent research hotspot.

Commercial adoption of semi-solid processing in automobiles began in the 1990s in the USA and Italy, with thixo-forging and thixo-HPDC prevalent from the 1990s to 2000s. Since 2010, China has seen rapid growth in application, with rheo-HPDC becoming the mainstream process. Applications are categorized into producing high-quality components and improving casting quality. Semi-solid processed components exhibit fewer defects, enabling heat treatment and achieving mechanical properties comparable to iron and steel, facilitating weight reduction (35-55% reduction compared to iron/steel components). Examples include torsion supports, control arms, brake calipers, and chassis brackets produced by Sliver Bases Die-Casting [43], engine brackets by Kovolis Hedvikov [44], and CAB mounts and muffler brackets by SAG Fueltech Sweden [33]. For improving casting quality, semi-solid HPDC reduces defects like gas bubbles, shrinkage, and tear cracks. GISSCO [45] and Runxingtai Electrical Equipment [46] utilize rheo-HPDC and ACSR rheo-HPDC, respectively, for components like pump bodies, housings, power converters, and electric control system parts.

Analysis of presented data:

The data presented in the review indicates a clear progression in semi-solid processing technology, with a shift towards rheo-route methods and HPDC for automotive applications. The adoption of semi-solid processing is driven by the need for lightweighting and high-quality components. The case studies and examples provided demonstrate the practical benefits of semi-solid processing in terms of weight reduction, improved mechanical properties, and enhanced casting quality. The emergence of additive manufacturing for semi-solid metals suggests future potential for even more complex and customized automotive components.

7. Conclusion:

Summary of Key Findings:

Semi-solid processing technology for aluminum alloys has matured over five decades, with diverse methods for metal preparation and component forming now available. Rheo-HPDC processes, particularly SEED, GISS, RSF, and ACSR, are increasingly utilized in the automotive industry for producing high-quality components and enhancing casting quality. The growing demand for lightweight vehicles is expected to further expand the application scale of semi-solid processing, especially for large automotive body parts.

Academic Significance of the Study:

This review provides a comprehensive academic resource summarizing the evolution and current state-of-the-art of semi-solid processing technology for aluminum alloys in automotive applications. It consolidates findings from numerous studies, offering valuable insights for researchers and experts in materials science, manufacturing, and automotive engineering.

Practical Implications:

The practical implications of this review are significant for automotive manufacturers seeking to adopt advanced lightweighting strategies. Semi-solid processing, particularly rheo-HPDC, presents a viable industrial solution for producing high-performance, complex-shaped aluminum components with reduced weight and improved quality. The review also highlights the potential of welding semi-solid processed parts as a novel approach for manufacturing large automotive body structures, offering a cost-effective alternative to ultrahigh vacuum die casting for large components.

Limitations of the Study and Areas for Future Research:

As a review paper, the limitations are inherent in the scope of the reviewed literature. The study is limited to the information available in the published domain. Future research directions include:

  • Further optimization and industrial scaling of rheo-route semi-solid processing techniques to enhance efficiency and reduce costs.
  • In-depth investigation of additive manufacturing of semi-solid metals for automotive applications, focusing on process control and material characterization.
  • Exploration of the welding and joining technologies for semi-solid processed aluminum components to enable the fabrication of large and complex automotive body structures.
  • Further research into the application of semi-solid processing for novel aluminum alloys and composite materials in automotive engineering.

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9. Copyright:

  • This material is Hongxing Lu, Zhengbai Liu, and Qiang Zhu's paper: Based on "Application of Aluminum Alloy Semi-Solid Processing Technology in Automobile: A Review".
  • Paper Source: https://doi.org/10.53941/ijamm0201005

This material was summarized based on the above paper, and unauthorized use for commercial purposes is prohibited.
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Tags: Al-Si alloy; ,aluminum alloy; ,aluminum alloys; ,CAD; ,Die casting; ,High pressure die casting; ,High pressure die casting (HPDC); ,Microstructure; ,Permanent mold casting; ,Sand casting