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1

Fabrication of a high wear resistance AA7075/AL2O3 composites via liquid metallurgy process

Sivaraman R., Jalil Abduladheem Turki, Aravindhan Surendar, Nan Zhao, Vini M. Heydari, Daneshmand S.

International Journal of Applied Mechanics and Engineering

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2022

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Vol. 27, no. 4

205--210

EN

In the present study, AA7075/Al2O3 composites have been fabricated via liquid metallurgy process. AA7075 alloy and Al2O3 particles were taken as the base matrix and reinforcements, respectively. Then, contents of 3 and 6 wt. % of Al2O3 subdivisions were added into the AA7075 matrix. To improve wettability and distribution, reinforcement particles were pre-heated to a temperature of 550°C for each composite sample. A hardened EN32 steel disc as the counter face was used to evaluate the wear rate pin-on-disc. The results showed that the wear rate of the AA/Al2O3 composites was smaller than that of the monolithic AA7075 samples. Finally, the worn surfaces of samples were investigated by SEM.

2

Investigation of Strain Inhomogeneity in Hexa-ECAP Processed AA7075

Öğüt Serkan, Kaya Hasan, Kentli Aykut, Özbeyaz Kerim, Şahbaz Mehmet, Uçar Mehmet

Archives of Metallurgy and Materials

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2021

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Vol. 66, iss. 2

431--436

EN

Severe Plastic Deformation (SPD) techniques have been used by researchers for last three decades in order to obtain Ultra-Fine Grained (UFG) materials. Equal Channel Angular Pressing (ECAP) is preferred more than other SPD techniques thanks to its high performance and practicability. Hexa Equal Channel Angular Pressing (Hexa-ECAP) – modified ECAP technique which enables to apply ECAP routes for cylindrical samples properly – was preferred in this study. Within the objective of this study, the effects of coefficient and ram velocity on the mean effective strain and strain inhomogeneity of Hexa-ECAP processed Al7075 aluminium alloy were investigated. Also, the effects of ram velocity and friction coefficient on hardness homogeneity were investigated benefitting from the similarity between the hardness distribution and the strain distribution.

3

Microstructure and mechanical properties of the AA7075 tube fabricated using shear assisted processing and extrusion (ShAPE)

Nazari Tiji Sobhan A., Asgharzadeh Amir, Park Taejoon, Whalen Scott A., Reza-E-Rabby Md, Eller Michael, Pourboghrat Farhang

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 2

85--94

EN

Shear-assisted processing and extrusion (ShAPE) experimental setup and tooling were adopted for extruding thin-walled AA7075 aluminum tube from as-cast non-homogenized billet material in a single run. The mechanical and microstructural characterizations were performed on the as-extruded tube through tensile, hardness, electron backscatter diffraction (EBSD), and energy dispersive spectroscopy (EDS) tests. The results showed that the ShAPE process developed a significantly refined microstructure with uniform and almost equiaxed grain structure on both hoop and axial cross-sections of the extrudate as well as through the thickness of the material. The pole figures and inverse pole figures of the EBSD data showed a strong shear texture development, and it was found out that axial shear is the dominant deformation mechanism in the regions near the inner surface of the tube, while combined axial and torsional shears are the two dominant modes of deformation near the outer surface of the extrudate. As for the mechanical properties, there was an increase of 150 and 73% in the yield and ultimate strengths of the tube produced using ShAPE process, respectively, and an 18% decrease in maximum uniform plastic elongation compared to the conventionally extruded AA7075-O tube.

4

Experimental characterization of heat transfer coefficients for hot stamping AA7075 sheets with an air gap

Xiao Wenchao, Zheng Kailun, Wang Baoyu, Yang Xiaoming

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 3

429--438

EN

The heat transfer coefficient (HTC) is critical for hot stamping and in-die quenching. The air gap at interface is a dominant factor affecting the HTC, which is normally resulted from initial tooling clearance and thinning of deformed aluminum sheet. To precisely determine the HTCs under different air gaps, this research performed a comprehensive investigation on determining HTCs between an AA7075 blank and H13 tool steel. Hot stamping experiments were performed with different air gaps enabling HTC values were determined. Using the experimentally calibrated HTC, a finite-element model for hot stamping a door beam was established, which was successfully verified using the experimentation. The good predictions showed the reliability of the HTC values under different air gap conditions.

5

Behaviors and modeling of thermal forming limits of AA7075 aluminum sheet

Xiao Wenchao, Wang Baoyu

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 1

134--143

EN

The aluminum hot stamping process has been widely studied to produce lightweight parts in automobile industry. As forming limit of aluminum sheet at elevated temperatures plays a vital role in judging stamping formability, this study aims at experimentally investigating the forming limits and establishing a constitutive model to predict them. In this study, isothermal deformation test (Nakajima test) of AA7075 was conducted to determine its forming limits at temperatures of 300–450 °C and stamping speeds of 13–40 mm/s. Based on the experimental results, a constitutive model considering continuum damage mechanics was established to predict the forming limits under different deformation conditions. It was found that the formability of the material is best at 400 °C, and a higher strain rate can improve formability slightly. The comparisons between model predictions and experimental results were evaluated; results indicated a good prediction accuracy of the model in describing forming limits of AA7075 at elevated temperatures. Moreover, comparison between different studies on the thermal forming limits of AA7075 was discussed in detail.

6

Challenges in Producing Reliable Tensile Properties by SIMA 7075

Erzi E., Gursoy O., Yüksel Ç.O.K., Kirtay S., Dispinar D.

Archives of Foundry Engineering

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2018

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Vol. 18, iss. 3

71--75

EN

Aluminium alloys are one of the preferred materials especially for land and air transportation because of their high strength and low-density properties. Although production using casting method is economical yet it has some disadvantages. Shrinkage which is occurred due to the density difference between the solid and liquid metal is prevented by feeders which need to be calculated. Liquid metal should be transferred to the mould without any turbulence. As a result, sprues are needed to be designed precisely. On the other hand, aluminium alloys can also be shaped by forging at semi-solid temperatures. There are some advantages compared to the traditional forging methods of improving die life due to the lower tonnage values. In this study, semi-solid produced 7075 aluminium alloy die filling capabilities were investigated. To achieve semisolid structure strain induced melt activated method (SIMA) was used. The desired structure was achieved at 635°C and 30 minutes of duration of heat treatment. After determining the optimum parameters, metallographic analysis, density calculations, porosity distribution and tensile tests were carried out. It was found that the reproducibility of SIMA produced 7075 alloy was quite low. A proper tensile test result was achieved only 7 of the total 15 tests and the mean value was 386 MPa. The main reason for this scattered in mechanical properties could be the chemical composition of the alloy and the rapid solidification of the liquid eutectic phases. It is important to define the best fitting process parameters and controlling them precisely will be the most important factors for future studies.

7

A study of interfacial heat transfer and its effect on quenching when hot stamping AA7075

Xiao W., Wang B, Zheng K., Zhou J., Lin J.

Archives of Civil and Mechanical Engineering

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2018

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Vol. 18, no. 3

723--730

EN

The aim of this research was to investigate the effects of contact pressure and lubrication on the interfacial heat transfer coefficient (IHTC) between AA7075 sheet and H13 tool steel and the in-die quenching performance in hot stamping. Firstly, a series of designed in-die quenching experiments were performed using different contact pressures, 0.05–30 MPa and lubrication conditions to determine the IHTC values using an efficient methodology. Secondly, temperature evolution of the tools and blank during the in-die quenching was investigated. Mechanical properties of material in-die quenched under different process conditions, were measured to determine their relation to quench conditions. The results have shown that IHTC values increased with increasing contact pressure and use of lubricant. A strength level of T6 condition could be obtained using a contact pressure greater than 5 MPa in the lubricated condition.

8

Comparision of Experimental and Simulated Weld Bead Geometry by Varying the Weld Speed in TIG Welded AA7075 Aluminium Alloy

Bosco Jude S., Jinu G. R., Arul Franco P.

Mechanics and Mechanical Engineering

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2016

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Vol. 20, nr 4

377--392

EN

In this present study, Aluminium Alloy material (AA7075) is selected as the investigation material in which TIG welding process was utilized for welding and the temperature analysis was carried out. The same was simulated using ANSYS software by finite element technique considering the characteristics and advantage of TIG welding process than other sources for welding of aluminium alloys. A travel heat source combined with body loads was designed by analyzing thermal physical parameters, latent heat of fusion of material. The weld model was created by using Solid modeling and direct generation technique. Residual control method was taken for precise node selection. The simulation was carried out by varying the welding speed process parameter of TIG welding and keeping current & voltage as constant. The quasisteady state temperature field of TIG welding was simulated with the FEA software (ANSYS) as well as experimental tests. The main objective of this work is to compare the experimentally obtained weld bead geometry parameters such as bead width and depth of penetration of AA7075 welded joint with simulated results from ANSYS software for various weld speeds. From the results it is indentified that for the sample welded at 120 mm/min is having higher weld bead geometry when compared to the samples welded at 130 mm/min and 140 mm/min. The lower bead geometry is obtained for the sample welded at 140 mm/min is due to the application of less heat energy as input. Similarly for 130 mm/min lower bead geometry is obtained because less heat energy is spent on joining. Joining of two metals or alloys is important in every aspect of engineering which leads to welding in an effective manner and carrying out the analysis. The experimental analysis shows that the model is showing good agreement with the experimental results. Comparison of the experimental and simulated results shows the maximum deviation of 6.24 % and 6.28 % is obtained for calculating the bead width and depth of penetration, respectively. Keywords: TIG welding, AA7075, Simulation, Weld Bead Geometry, ANSYS.

9

W-temper forming of aa7075 aluminum alloys as an alternative to the warm and hot stamping

Saenz de Argandona E., Galdos L., Ortubay R., Mendiguren J., Agirretxe X.

Computer Methods in Materials Science

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2015

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Vol. 15, No.1

51--57

EN

As important light-weight structure material, aluminum alloys have been widely used in automotive and aerospace industries. In the last years, the manufacturing of parts with high strength and good dimensional accuracy has become the main objective in industrial applications. Within the available aluminum alloys, the 7xxx series has attract the interest of the industrial designers due to the high yield strength and ultimate tensile strength they present. However, the formability of these alloys in as-received industrial condition is very poor at room temperature and various studies are being carried out to develop efficient warm and hot forming processes to form them industrially using heated tools. In the present paper, the W-temper forming is studied as an alternative to the warm and hot forming processes. Heat treatment temperatures and critical times are presented and an industrial B-Pillar is formed to validate the new process. In the last chapter, the final mechanical properties of the part are reported, before and after a virtual e-coat process where the W-temper forming is compared with a hot stamping process.

PL

Stopy aluminium, jak ważny, lekki materiał konstrukcyjny, są szeroko stosowane w przemyśle motoryzacyjnym i lotniczym, ostatnich latach, wytwarzanie części o wysokich własnościach wytrzymałościowych i dużej precyzji stało się jednym z głównych zastosowań przemysłowych. Spośród dostępnych stopów aluminium, seria 7xxx jest szczególnie interesująca dla projektantów-przemysłowych, ze względu na wysoką granicę plastyczności wytrzymałość na rozciąganie. Jednakże, plastyczne kształtowanie tego typu stopów w warunkach przemysłowych, w temperaturze pokojowej jest bardzo ograniczone. Stąd prowadzonych jest wiele badań nad opracowaniem efektywnego kształtowania stopów aluminium w procesach na ciepło i gorąco z wykorzystaniem podgrzewanych narzędzi, mogących mieć zastosowania przemysłowe. W niniejszej pracy analizowano proces kształtowania zwany W-temper jako alternatywę dla odkształcania na ciepło lub gorąco.. Walidację nowego procesu wytwarzania przedstawiono dla wybranej, rzeczywistej części produkowanej dla przemysłu motoryzacyjnego, fragmentu słupka B. W ostatniej części pracy omówiono końcowe własności mechaniczne produktu, gdzie kształtowanie typu W-temper zostało porównane z procesem tłoczenia na gorąco.

10

Effect of post-weld aging on the mechanical and microstructural properties of friction stir welded aluminum alloy 7075

Yeni C., Sayer S., Ertugrul O., Pakdil M.

Archives of Materials Science and Engineering

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2008

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Vol. 34, nr 2

105-109

EN

Purpose: of this paper is to investigate the effect of post-weld artificial aging on the friction stir welding of Aluminum Alloy 7075 (AA 7075) for a welding condition of 1600 rpm and 100 mm/min using right and left helical screwed pins for two different shoulder diameters. Design/methodology/approach: The method followed is that first artificial aging has been carried out as 24 hours at 125°C. Afterwards, in order to study the effect of post-weld aging on tool geometry, microstructural examination, hardness measurements and room temperature tensile tests have been carried out. Findings: The results show that left helical screw yields higher mechanical properties and hardness values compared to right helical screw when tested at the same shoulder diameter. It has been observed that post weld aging process compensates the hardness decrease observed in as-welded joints; no significant decrease in hardness is obtained throughout the weld region. Research limitations/implications: For future work it can be suggested to vary the post weld aging condition, such as 12 hours at 125°C. Welding and rotation speeds are other parameters affecting the microstructural and mechanical properties; therefore the effect of varying these parameters should be considered. Practical implications: This study has practical implications and direct applicability. It indicates that helix angle rather than shoulder diameter directly affects the quality of the joint. At certain post weld aging conditions, for obtaining a sound welded joint the right tool selection will be of critical importance. Originality/value: The authors have examined the effect of post weld aging for different helix angles and shoulder diameters. It is believed that examination of the effect of the variation of these parameters on the joint quality provides originality to this study.