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Metals
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Metal Forming Technologies for Producing High-Strength and Lightweight Parts
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Metal Forming Technologies for Producing High-Strength and Lightweight Parts

A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Metal Casting, Forming and Heat Treatment".

Deadline for manuscript submissions: closed (31 October 2021) | Viewed by 17896

Special Issue Editor

Prof. Dr. Heung-Kyu Kim

E-Mail Website
Guest Editor
Department of Automotive Engineering, Kookmin University, 77, Jeongneung-ro, Seongbuk-gu, Seoul 02707, Korea
Interests: crystal plasticity; warm forming; hot stamping; composite forming; finite element analysis; optimization; hyperelasticity; multiscale analysis

Special Issue Information

Dear Colleagues,

High-strength and lightweight technologies for automobiles and aircraft are very important for improving safety, as well as energy efficiency. There are various methods of achieving high strength and lightweight by using metallic materials. High-strength steel can be formed by methods such as roll forming and multi-stage forming that can overcome the low forming limits, despite the occurrence of large springback. As an alternative, hot stamping is widely used in mass production. Hot stamping can manufacture parts with complex shapes while increasing strength and reducing the springback of parts. The successful implementation of hot stamping requires advanced design and optimization techniques that take into account heat transfer, phase transformation, and process conditions. However, to date, problems such as reduced part strength due to lack of heat transfer performance between the die and material, excessive cost for trimming and hot stamping die, and the complexity of process design optimization have not been sufficiently solved.

Lightweight metals, such as aluminum, magnesium, and titanium, may be used instead of steel to manufacture lightweight parts while securing required strength. In order to improve the low formability of lightweight metals, warm or hot forming methods have been applied. For example, in the case of magnesium, a warm forming is widely applied to improve formability, and in the case of aluminum, a method of increasing the part strength to a steel level through hot forming, in combination with hot stamping, has recently been attempted. However, it is still necessary to understand the material characteristics of lightweight metals that are more complex than steels, and to develop optimal warm/hot forming technologies.

Various research articles on metal forming technologies covering materials, forming processes and die technologies related to weight reduction and strength improvement are welcome.

Prof. Dr. Heung-Kyu Kim
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Metals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • high-strength
  • lightweight
  • hot stamping
  • springback
  • optimization
  • heat transfer
  • phase transformation
  • die
  • warm forming

Published Papers (9 papers)

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12 pages, 6279 KiB  
Article
Evaluation of Fatigue Characteristics of Aluminum Alloys and Mechanical Components Using Extreme Value Statistics and C-Specimens
by Jungsub Lee, Sang-Youn Park and Byoung-Ho Choi
Metals 2021, 11(12), 1915; https://0-doi-org.brum.beds.ac.uk/10.3390/met11121915 - 27 Nov 2021
Cited by 5 | Viewed by 3253
Abstract
In this study, the fatigue characteristics of aluminum alloys and mechanical components were investigated. To evaluate the effect of forging, fatigue specimens with the same chemical compositions were prepared from billets and forged mechanical components. To evaluate the cleanliness of the aluminum alloys, [...] Read more.
In this study, the fatigue characteristics of aluminum alloys and mechanical components were investigated. To evaluate the effect of forging, fatigue specimens with the same chemical compositions were prepared from billets and forged mechanical components. To evaluate the cleanliness of the aluminum alloys, the cross-sectional area of specimens was observed, and the maximum inclusion sizes were obtained using extreme value statistics. Rotary bending fatigue tests were performed, and the fracture surfaces of the specimens were analyzed. The results show that the forging process not only elevated the fatigue strength but also reduced the scatter of the fatigue life of aluminum alloys. The fatigue characteristics of C-specimens were obtained to develop finite-element method (FEM) models. With the intrinsic fatigue properties and strain–life approach, the FEM analysis results agreed well with the test results. Full article
(This article belongs to the Special Issue Metal Forming Technologies for Producing High-Strength and Lightweight Parts)
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18 pages, 5529 KiB  
Article
A Study on the Effect of Process and Material Variables on the Hot Stamping Formability of Automotive Body Parts
by Kang Ho You and Heung-Kyu Kim
Metals 2021, 11(7), 1029; https://0-doi-org.brum.beds.ac.uk/10.3390/met11071029 - 26 Jun 2021
Cited by 6 | Viewed by 2507 | Correction
Abstract
Hot stamping is a method capable of manufacturing high-strength automotive body parts by inducing a martensitic phase transformation through forming and die quenching after heating a metal sheet into a high temperature austenite phase. However, it is not easy to solve various formability [...] Read more.
Hot stamping is a method capable of manufacturing high-strength automotive body parts by inducing a martensitic phase transformation through forming and die quenching after heating a metal sheet into a high temperature austenite phase. However, it is not easy to solve various formability problems occurring in the hot stamping process due to the complexity of the process and material behavior during high temperature forming. In this study, fracture-related forming limits and martensite phase ratio were selected as criteria for evaluating hot stamping formability. First, a hot stamping test was performed on a T-type part that simplified the B-pillar, an automotive body part, and the fracture behavior according to the temperature and thickness of the sheet blank was investigated. Additionally, forming analysis was performed on the hot stamping process of mass-produced B-pillar parts by varying the temperature of the sheet blank, the thickness of the sheet blank, the die-blank friction coefficient, and the strain-rate sensitivity of material among various process and material variables. Based on the analysis results, the effect of each process and material variable on the hot stamping formability of B-pillar parts was quantitatively analyzed. By utilizing the results of this study, it will be possible to solve the formability problem that occurs in the mass-production hot stamping process for automotive body parts and improve the quality of parts in the future. Full article
(This article belongs to the Special Issue Metal Forming Technologies for Producing High-Strength and Lightweight Parts)
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9 pages, 4290 KiB  
Article
Forming a Flanged Hole When Quenching Press-Hardened Steel for Mechanical Fastening
by Yongjun Jeon, Hyunseok Choi and Dongearn Kim
Metals 2021, 11(5), 721; https://0-doi-org.brum.beds.ac.uk/10.3390/met11050721 - 28 Apr 2021
Cited by 1 | Viewed by 1998
Abstract
The recent stringent regulations on vehicle safety and reducing CO2 emissions have led to a continuous increase in the application of press-hardened steel (PHS) in automobiles. Similar to other high-strength steels, assembling PHS components using the common welding techniques employed in automotive [...] Read more.
The recent stringent regulations on vehicle safety and reducing CO2 emissions have led to a continuous increase in the application of press-hardened steel (PHS) in automobiles. Similar to other high-strength steels, assembling PHS components using the common welding techniques employed in automotive production lines is significantly difficult because of the surface coating layers and the additives within. This difficulty in post-processing, attributed to its high strength, also limits the mechanical fastening of PHS components. Therefore, this study aims to develop a process for forming a structure enabling mechanical fastening by sequentially applying piercing and hole-flanging operations during the hot stamping process. Our experimental apparatus was designed to perform the hole-flanging operation after the piercing operation within a single stroke at a specific temperature during the quenching process of PHS. At high temperatures of 440 °C or higher, the hole-flanging process was conducted in a direction opposite to that of the piercing operation for creating the pilot hole. An extruded collar with a height of 8.0 mm and a diameter of 17.5 mm was achieved, which is hole expansion ratio(HER) of 82.5%. Full article
(This article belongs to the Special Issue Metal Forming Technologies for Producing High-Strength and Lightweight Parts)
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10 pages, 5422 KiB  
Article
Determination of Plastic Anisotropy of Extruded 7075 Aluminum Alloy Thick Plate for Simulation of Post-Extrusion Forming
by Dae-Kwan Jung, Seong-Ho Ha, Heung-Kyu Kim and Young-Chul Shin
Metals 2021, 11(4), 641; https://0-doi-org.brum.beds.ac.uk/10.3390/met11040641 - 14 Apr 2021
Cited by 2 | Viewed by 1801
Abstract
In this study, the plastic anisotropy distribution of an extruded 7075 aluminum alloy thick plate was evaluated through small-cube compression tests. The extruded plate with a thickness of 15 mm was divided into five layers in order to verify the difference in plastic [...] Read more.
In this study, the plastic anisotropy distribution of an extruded 7075 aluminum alloy thick plate was evaluated through small-cube compression tests. The extruded plate with a thickness of 15 mm was divided into five layers in order to verify the difference in plastic anisotropy along the thickness direction of the extruded thick plate. Small-cube specimens with a side length of 1 mm were extracted from each layer and subjected to compression tests in each direction to evaluate the directional r-values of the extruded material. The r-values were applied to Hill’s quadratic yield criterion to calculate the six coefficients for each layer. To consider the plastic anisotropy in the thickness direction, a finite element model divided into five layers in the thickness direction was applied. Upsetting tests were conducted to verify the accuracy of the finite element analysis using cube specimens with a side length of 15 and 10.6 mm, and the results of the finite element analysis and the upsetting test were compared and analyzed against each other. Consequently, the finite element analyses were precisely simulated the upsetting test results. Full article
(This article belongs to the Special Issue Metal Forming Technologies for Producing High-Strength and Lightweight Parts)
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10 pages, 5018 KiB  
Article
Effect of Combined Extrusion and Rolling Parameters on Mechanical and Corrosion Properties of New High Strength Al-Mg Alloy
by Kweon-Hoon Choi, Bong-Hwan Kim, Da-Bin Lee, Seung-Yoon Yang, Nam-Seok Kim, Seong-Ho Ha, Young-Ok Yoon, Hyun-Kyu Lim and Shae-Kwang Kim
Metals 2021, 11(3), 445; https://0-doi-org.brum.beds.ac.uk/10.3390/met11030445 - 08 Mar 2021
Cited by 1 | Viewed by 1463
Abstract
High strength Al-Mg alloy is an attractive material that has the characteristic of increasing both strength and elongation by adding more solute Mg. However, there is a limitation in the oxidation issue during the casting process when it contains high amounts of solute [...] Read more.
High strength Al-Mg alloy is an attractive material that has the characteristic of increasing both strength and elongation by adding more solute Mg. However, there is a limitation in the oxidation issue during the casting process when it contains high amounts of solute Mg. New Al-Mg alloy was developed using Mg+Al2Ca master alloy by making a stable CaO/MgO mixed layer that no significant oxidation occurred. Here, the intergranular corrosion (IGC), electrochemical, and mechanical properties of new Al-Mg alloys fabricated through a combined process of extrusion and cold rolling were studied after the specimens went through artificial aging heat treatment at 200 °C. The results show that the grain size and the volume fraction of anodic β-precipitation (Mg2Al3) forming on the grain boundary influence the intergranular corrosion results. Corrosion potential and current density were achieved by potentiodynamic polarization electrochemical test. The results show that corrosion potential remains irrespective of the manufacturing process, while current density increases with artificial aging treatment. Both hardness and tensile mechanical properties decrease on cold rolled specimens after the heat treatment, while increase in extrusion and annealed specimens. Full article
(This article belongs to the Special Issue Metal Forming Technologies for Producing High-Strength and Lightweight Parts)
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18 pages, 23931 KiB  
Article
Stretch Forming Behavior and Constitutive Equation of a Modified 5083 Alloy with High Mg Content at Elevated Temperatures
by Seung-Yoon Yang, Da-Bin Lee, Kweon-Hoon Choi, Nam-Seok Kim, Seong-Ho Ha, Bong-Hwan Kim, Young-Ok Yoon, Hyun-Kyu Lim, Shae K. Kim and Young-Jig Kim
Metals 2021, 11(3), 410; https://0-doi-org.brum.beds.ac.uk/10.3390/met11030410 - 03 Mar 2021
Cited by 5 | Viewed by 1708
Abstract
For the purpose of applying a modified 5083 alloy (New 5083M alloy) with high Mg content in various automotive sheet parts, the stretch forming behavior of the 5083M alloy was studied in tensile mode at a wide range of processing conditions. The tensile [...] Read more.
For the purpose of applying a modified 5083 alloy (New 5083M alloy) with high Mg content in various automotive sheet parts, the stretch forming behavior of the 5083M alloy was studied in tensile mode at a wide range of processing conditions. The tensile tests were conducted by using a tensile test machine under the temperature ranges of 100–400 °C and the strain rate ranges of 0.001–1 s−1. The test results showed that the 5083M alloy has superior mechanical properties to that of the commercial 5083 alloy at elevated temperatures. The microstructure before and after the stretch forming was analyzed using optical microscope (OM) equipped with a polarizing filter and electron backscattered diffraction (EBSD) unit. Deformed microstructure was observed under low temperature conditions and dynamic recrystallized microstructure under high temperature conditions. However, regardless of microstructure evolution, developed deformation textures were distributed in orientation distribution functions (ODF) images. In addition, at high temperature and low strain rate condition, complex shaped cavities which were detrimental to mechanical properties appeared at the grain boundary and grain triple junction. Based on the test results data, a constitutive equation predicting the deformation behavior of the 5083M alloy was derived. The calculated curves by the constitutive equation were compared with the measured curves by experiment and agreed well. Full article
(This article belongs to the Special Issue Metal Forming Technologies for Producing High-Strength and Lightweight Parts)
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11 pages, 8289 KiB  
Article
Hot Compression Behavior of New Al-6Mg and Al-8Mg Alloy with Improved Hot Workability Fabricated by Direct Chill Casting Method
by Nam-Seok Kim, Kweon-Hoon Choi, Seung-Yoon Yang, Seong-Ho Ha, Young-Ok Yoon, Bong-Hwan Kim, Hyun-Kyu Lim, Shae K. Kim and Soong-Keun Hyun
Metals 2021, 11(2), 288; https://0-doi-org.brum.beds.ac.uk/10.3390/met11020288 - 07 Feb 2021
Cited by 5 | Viewed by 1721
Abstract
A hot compression test of new Al-6Mg and Al-8Mg alloys was conducted to understand the dynamic recrystallization (DRX) behavior by Mg contents. To investigate the hot workability of Al-Mg with high Mg contents, the hot deformation behavior of Al-6Mg and Al-8Mg alloys was [...] Read more.
A hot compression test of new Al-6Mg and Al-8Mg alloys was conducted to understand the dynamic recrystallization (DRX) behavior by Mg contents. To investigate the hot workability of Al-Mg with high Mg contents, the hot deformation behavior of Al-6Mg and Al-8Mg alloys was analyzed by a hot compression test in the temperature range of 300–450 °C, and the strain rate range of 10−3–100/s. Subsequently, high-temperature deformation behavior was investigated through the processing map and microstructure observation. In this study, the results have shown that, as the Mg contents increase, the maximum and yield strength increase while rapid flow softening after the peak strain has been observed due to accelerated dynamic recrystallization (DRX). Finally, the increase of Mg contents affects an increase of heat dissipation efficiency to be an indicator of regular deformation. Full article
(This article belongs to the Special Issue Metal Forming Technologies for Producing High-Strength and Lightweight Parts)
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14 pages, 5874 KiB  
Article
Influence of Addition of Al and Ti Solutes and Variable Processing Conditions on Mechanical and Electrical Properties of Cu-Cr Alloys
by Chang-Hee Cho, Jesik Shin, Dongearn Kim and Hoon Cho
Metals 2021, 11(1), 39; https://0-doi-org.brum.beds.ac.uk/10.3390/met11010039 - 26 Dec 2020
Cited by 2 | Viewed by 1638
Abstract
To apply the electric component with high efficiency, the softening problem of material should be improved. Cu-Cr alloys are recognized to be proper materials to be applied. However, the softening problem has not been solved yet. In this study, the effect of Ti [...] Read more.
To apply the electric component with high efficiency, the softening problem of material should be improved. Cu-Cr alloys are recognized to be proper materials to be applied. However, the softening problem has not been solved yet. In this study, the effect of Ti and Al on mechanical property and electrical conductivity in Cu-Cr alloy was investigated. Cr content is designed to up to 0.25 wt.% in order to be expected to improve electrical conductivity. During fabrication processing, microstructure identification, Cr concentration, lattice parameter, and micro-hardness in copper matrix were measured. Then, aging condition was investigated. Resistance about over-aging is increased compared to Cu-Cr and Cu-Cr-Al alloy added to Ti. The hardness and electrical conductivity are discussed by the working conditions and heat treatment, such as rolling, solid-solution treatment, and aging process, which improve the formability also at the optimum condition. Moreover, the role of Ti contents is studied. In the Cu-Cr alloys, the addition of both Al and Ti contents keeps the hardness from being reduced. As a result, the precipitation of Cr particles and the obstacle by Al and Ti contents to be softened are observed in this study. Full article
(This article belongs to the Special Issue Metal Forming Technologies for Producing High-Strength and Lightweight Parts)
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7 pages, 2774 KiB  
Correction
Correction: You, K.H.; Kim, H.-K. A Study on the Effect of Process and Material Variables on the Hot Stamping Formability of Automotive Body Parts. Metals 2021, 11, 1029
by Kang Ho You and Heung-Kyu Kim
Metals 2022, 12(7), 1100; https://0-doi-org.brum.beds.ac.uk/10.3390/met12071100 - 28 Jun 2022
Viewed by 910
Abstract
Data and expressions provided by Hyundai Steel, which are not intended to be disclosed, were included in the figures and text [...] Full article
(This article belongs to the Special Issue Metal Forming Technologies for Producing High-Strength and Lightweight Parts)
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