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Development of ultrafine grained Al–Zn–Mg–Cu alloy by equal channel angular pressing: microstructure, texture and mechanical properties

Ghosh Abhishek, Ghosh Manojit, Gudimetla Kondaiah, Kalsar Rajib, Kestens Leo A. I., Kondaveeti Chandra Sekhar, Pugazhendhi Bhagat Singh, Ravisankar Balasubramanian

Archives of Civil and Mechanical Engineering

2020

Vol. 20, no. 1

82--98

In this article, an effort has been made to investigate the evolution of microstructure, texture and mechanical properties of AA 7075 alloy during equal channel angular pressing (ECAP) by route BC at room temperature at a pressing speed of 1 mm/min. Transmission electron microscopy (TEM) revealed the presence of rod-like (MgZn2) precipitates in annealed conditions which were broken after two ECAP passes along with remarkable grain refinement due to high imposed strain after the second pass. After two consecutive ECAP passes, hardness, yield strength, and tensile strength of the alloy increased significantly in comparison to initial annealed condition. The fraction of high angle boundaries (HABs) and grain misorientation angle significantly increased after ECAP passes compared to the initial condition. Texture measurements were performed by X-ray diffractometer (XRD), on TD plane (parallel to extrusion direction). Texture results revealed the dominance of Cθ and A∗2θ components after the first pass and the presence of strong Bθ, B¯θ and A¯θ components along with weaker A∗2θ,Cθ components after the second pass. Scanning electron microscopy (SEM) revealed that the average dimple size was gradually reduced with increasing the ECAP passes.

Hybrid friction stir processing with active cooling approach to enhance superplastic behavior of AA7075 aluminum alloy

Patel Vivek, Badheka Vishvesh, Li Wenya, Akkireddy Satyaprasad

Archives of Civil and Mechanical Engineering

2019

Vol. 19, no. 4

1368--1380

Friction stir processing (FSP) with active cooling approach can be considered as one of the variants of the FSP in order to enhance superplastic behavior. In this study, high strength AA7075 alloy was subjected to normal and hybrid FSP at different cooling medium such as compressed air, water, and CO2 to obtain a variety of cooling rate during the process. Hybrid FSP samples were produced without any processing flaws at a lower processing temperature in comparison to normal FSP sample. Among the hybrid FSP samples, CO2 cooling sample was produced at the lowest processing temperature. Optical and electron microscopy confirmed that microstructures of all the samples were characterized by fine equiaxed grain in the stir zone (SZ). Reduction of grain size in hybrid FSP samples was found due to higher cooling rate, which prevented the coarsening of grains in the SZ. Improvement in grain refinement was observed in the order of normal (4.12 μm), compressed air (3 μm), water (2.64 μm), CO2 (1.96 μm) FSP samples. All FSP samples obtained the superplastic elongation. The highest elongation of 572% was achieved for CO2 cooling sample due to the finest grained microstructure produced at the lowest heat input during FSP.

Własności trybologiczne materiałów kompozytowych na osnowie stopu aluminium 7075 umacnianych włóknami Al2O3

Naplocha K., Kaczmar J. W.

Archives of Foundry Engineering

2011

Vol. 11, iss. 2 spec.

153--158

Badano odporność na zużycie ścierne materiałów kompozytowych na osnowie stopu aluminium 7075 umacnianych włóknami Al2O3 Saffil. Pomiary przeprowadzono metodą pin-on-disc w warunkach tarcia suchego dociskając próbki do obracającej się żeliwnej tarczy. Określono wpływ ciśnienia wywieranego przez próbki oraz ukierunkowania włókien, w stosunku do powierzchni ścieranej na stopień zużycia. Materiały wytwarzano metodą prasowania w stanie ciekłym nasycając stopem aluminium 7075 kształtki ceramiczne z włókien Saffil o porowatości 80-90%. Odporność na zużycie materiałów kompozytowych, w stosunku do nieumocnionego stopu 7075, była nieznacznie gorsza przy mniejszym ciśnieniu 0,8MPa wywieranym przez próbkę z kompozytu na żeliwną tarczę. Pod większym ciśnieniem 1,2 MPa odporność stopu nieumocnionego była jeszcze lepsza, a ukierunkowanie włókien w materiałach kompozytowych nie miało większego znaczenia na zużycie. Zaobserwowano również znaczne zużycie przeciwpróbki, gdyż zużyty materiał kompozytowy wraz z rozdrobnionymi włóknami Al2O3 pełnił rolę ścierniwa. Wzrost odporności na ścieranie materiałów kompozytowych na osnowie stopu 7075 uzyskano po zastosowaniu umocnienia zawierającego oprócz włókien Al2O3 również włókna C.

Wear resistance of 7075 aluminium alloy based composite materials reinforced with Al2O3 Saffil fibres was investigated. The measurements of wear were performed applying the pin-on-disc method at dry friction conditions with the gray iron counterpart. The effects of pressure of composite samples on the counterpart made of gray iron and the orientation of fibers in relation to the friction surface on wear rate were determined. The materials were produced by squeeze casting method where 80-90% porous ceramic preform were infiltrated. After T6 heat treatment hardness increased about 50-60% both for unreinforced alloy and composites containing strengthening Saffil fibres. Wear resistance of composite materials in relation to the unreinforced 7075 alloy was slightly worse at lower pressure of 0.8 MPa. Under higher pressure of 1.2 MPa wear resistance of unreinforced 7075 alloy was even better whereas no effect of orientation of fibers on wear in composite materials was observed. Additionally, significant wear of counterface in the presence of debris with fragmented Al2O3 fibres as abrasives was observed. Wear resistance improvement of composite materials was obtained when with alumina Saffil fibres Carbon C fibres in the preforms were applied.