Tearing mechanism for high-strength Al–Zn–Mg–Cu alloys in hot extrusion

Ngernbamrung, Sukunthakan; Funazuka, Tatsuya; Takatsuji, Norio; Murakami, Satoshi; Dohda, Kuniaki

doi:10.2464/jilm.68.660

Cited by 5 publications

(11 citation statements)

References 10 publications

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“…Figure 13 shows the tearing size-stroke diagram for various die coatings. In the previous study [8], it was shown that tearing increased with the stroke, which is consistent with the obtained result. Furthermore, the tearing depth increases with the stroke for all extrusion conditions, but the tearing depth of the AlCrN die is smaller than those of the nitriding, TiAlN, and DLC dies.…”

Section: Effect Of Die Coating On Tearing Of A7075 During Hot Extrusionsupporting

confidence: 92%

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Effect of die coating on surface crack depth of hot extruded 7075 aluminum alloy

et al. 2022

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The aluminum alloys belonging to the 7000 series are high-strength alloys used in a wide variety of products for weight reduction. They are primarily used in the field of transportation and aerospace. Among these, the A7075 alloy has the highest strength and is expected to be applicable in a wide range of fields, such as aircraft components and sports equipment. However, it has high deformation resistance and is prone to surface defects, which is called tearing. Tearing typically occurs at high temperatures and high ram speeds, and adversely affects productivity. The localized melting of Zn and additive compounds, due to the heat generated during the process, is considered to cause tearing. In this study, the effect of friction, heat, and tearing at the tool—metal interface was mitigated by improving the die surface quality. The reduced friction eliminated recrystallization by preventing the temperature from increasing to recrystallization temperature. In addition, an AlCrN coating was adopted instead of nitriding to improve the die surface quality. The tearing size and heat generated when using the AlCrN coating were found to be limited. Moreover, the grain size observed in the tearing region on the extruded surface was small. The simulations using the shear friction coefficient m observed from friction tests indicate that the use of the AlCrN coating improved the material flow. Thus, the AlCrN coating is considered effective for reducing friction at the interface and preventing the recrystallization of the extruded surface. From the aforementioned results, it can be inferred that a die coating can reduce the tearing sensitivity and increase the productivity of the A7075 alloy.

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Section: Effect Of Die Coating On Tearing Of A7075 During Hot Extrusionsupporting

confidence: 92%

“…Our previous studies showed that tearing is more likely to occur under high-temperature and highvelocity conditions [8]. We have reported that tearing is caused by the segregation and localized melting of soluble intermetallic compounds containing Zn and Mg in the crystalline structure.…”

Section: Introductionmentioning

confidence: 96%

Effect of die coating on surface crack depth of hot extruded 7075 aluminum alloy

et al. 2022

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“…The tearing depth of extrudate with and without cooling was about 1.50-300 µm, and 100-200 µm, respectively. The tearing occurs in the coarsened recrystallized microstructure layer at the edge of extrudate due to the heat generated during processing, which leads to crack propagation [4][5]. The cooling of the extrudate also inhibited the coarsening of the crystalline microstructure at the extrudate edge, which is thought to have reduced the tearing depth.…”

Section: Resultsmentioning

confidence: 99%

Effect of Temperature on Surface Cracking Defects in AA7075 Hot Extrusion

Funazuka

Dohda²,

Takatsuji

et al. 2022

KEM

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Aluminum alloys in the 7000 series are high-strength alloys that are used in a wide variety of products in the transportation equipment and aerospace fields to reduce weight. In particular, the A7075 alloy has the highest strength and is expected to find further applications in a wide range of fields such as aircraft parts and sporting goods. However, low productivity is a problem due to its high deformation resistance, tendency to produce surface defects called tearing on the product surface, and short tool life. Tearing tends to occur under high temperature and high speed conditions, and is thought to be caused by local melting of Zn, an additive element, due to heat generation in processing. In this study, to improve the productivity of A7075 alloy, the profile was cooled during extrusion to prevent recrystallization of extrudate surface grains due to processing heat and to prevent processing heat during forming. In order to investigate the cooling effect, hot extrusion simulation was conducted. The cooling effect successfully suppressed the occurrence of tearing. These results indicate that cooling the extrudate during forming reduces the effect of heat generation during forming and prevents recrystallization of the extrudate surface grains and local melting of Zn.

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“…In addition, AA7075 is one of the least deformable aluminum alloys and has high flow stress, which significantly limits the extrusion speed from 0.8 to 2.0 m/min. In our previous research, we reported that tearing was caused by low-melting intermetallic compounds containing magnesium (Mg) and zinc (Zn) [3]. It reported that the intermetallic compound with a low melting point locally melted due to the heat generated by the forming process.…”

Section: Introductionmentioning

confidence: 99%

Phenomena of tool adhesion at elevated temperature in V-groove friction test of AA7075

Funazuka

2023

Materials Research Proceedings

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Abstract. 7000 series aluminum alloys are high-strength alloys used in various lightweight products in the transportation equipment and aerospace industries. AA7075 extrusions are expected to find further applications in multiple fields, including aircraft parts, automotive parts, and sporting goods. However, the high deformation resistance and surface cracking defects caused by tool galling and adhesion have resulted in extremely low productivity. In this study, the V-groove compression test was proposed as a method to determine the coefficient of friction in hot metal forming. Using AA7075 as the experimental material, what did the V-groove compression test at various temperatures to compare the results with calibration curves created from the numerical analysis and observe the growth of adhesion.

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Tearing mechanism for high-strength Al–Zn–Mg–Cu alloys in hot extrusion

Cited by 5 publications

References 10 publications

Effect of die coating on surface crack depth of hot extruded 7075 aluminum alloy

Effect of die coating on surface crack depth of hot extruded 7075 aluminum alloy

Effect of Temperature on Surface Cracking Defects in AA7075 Hot Extrusion

Phenomena of tool adhesion at elevated temperature in V-groove friction test of AA7075

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