Kourosh Karimi Taheri

Bio: Kourosh Karimi Taheri is an academic researcher from Northeastern University. The author has contributed to research in topics: Ultimate tensile strength & Brittleness. The author has an hindex of 1, co-authored 2 publications receiving 120 citations.

The Effect of Prestrain Temperature on Kinetics of Static Recrystallization, Microstructure Evolution, and Mechanical Properties of Low Carbon Steel

Abstract: In this research, the samples of a low carbon steel sheet were rolled up to a thickness prestrain of 67% at three different temperatures consisted of room, blue brittleness, and subzero temperature. Microhardness, SEM, and tensile tests were carried out to evaluate the static recrystallization kinetics defined by the Avrami equation, microstructural evolution, and mechanical properties. It was found that the Avrami exponent is altered with change in prestrain temperature and it achieves the value of 1 to 1. 5. Moreover, it was indicated that prestraining at subzero temperature followed by annealing at 600 °C leads to considerable enhancement in tensile properties and kinetics of static recrystallization compared to room and blue brittleness temperatures. The prestraining at blue brittleness temperature followed by annealing treatment caused, however, a higher strength and faster kinetics compared with that at room temperature. It was concluded that although from the steel ductility point of view, the blue brittleness temperature is called an unsuitable temperature, but it can be used as prestraining temperature to develop noticeable combination of strength and ductility in low carbon steel.

The Advancement of 7XXX Series Aluminum Alloys for Aircraft Structures: A Review

Abstract: 7XXX series aluminum alloys (Al 7XXX alloys) are widely used in bearing components, such as aircraft frame, spars and stringers, for their high specific strength, high specific stiffness, high toughness, excellent processing, and welding performance. Therefore, Al 7XXX alloys are the most important structural materials in aviation. In this present review, the development tendency and the main applications of Al 7XXX alloys for aircraft structures are introduced, and the existing problems are simply discussed. Also, the heat treatment processes for improving the properties are compared and analyzed. It is the most important measures that optimizing alloy composition and improving heat treatment process are to enhance the comprehensive properties of Al 7XXX alloys. Among the method, solid solution, quenching, and aging of Al 7XXX alloys are the most significant. We introduce the effects of the three methods on the properties, and forecast the development direction of the properties, compositions, and heat treatments and the solution to the corrosion prediction problem for the next generation of Al 7XXX alloys for aircraft structures. The next generation of Al 7XXX alloys should be higher strength, higher toughness, higher damage tolerance, higher hardenability, and better corrosion resistance. It is urgent requirements to develop or invent new heat treatment regime. We should construct a novel corrosion prediction model for Al 7XXX alloys via confirming the surface corrosion environments and selecting the accurate and reliable electrochemical measurements.

On the PEO treatment of cold sprayed 7075 aluminum alloy and its effects on mechanical, corrosion and dry sliding wear performances thereof

Abstract: The plasma electrolytic oxidation (PEO) process was used to deposit an alumina coating on a cold sprayed 7075 aluminum alloy to improve the surface properties. The phase compositions, microstructures, basic mechanical properties, as well as the corrosion and the dry sliding wear resistance of cold sprayed 7075 aluminum alloy before and after PEO treatment, were investigated. The results show that a single-layered dense alumina coating with a thickness of ~15–20 μm and hardness of 1353 HV0.01 is realizable on the cold sprayed 7075 aluminum alloy by PEO treatment aided by an aluminate electrolyte. The corrosion current density and wear rate of the alumina PEO coating were 6.27 × 10−7 A/cm2 and 1.22 × 10−6 mm3/N·m respectively, which were three and two orders of magnitude lower compared to the uncoated rolled 7075 aluminum alloy (T6) substrate, thus highlighting the excellent wear and corrosion resistance of the PEO treated cold sprayed Al alloy surface.

Effect of Ag on aging precipitation behavior and mechanical properties of aluminum alloy 7075

Abstract: Effects of Ag addition on the age hardening and precipitation behavior of aluminum alloy 7075 were investigated. The transmission electron microscopy (TEM) and atom probe tomography (APT) were used to study the aggregate distribution and identify the role of Ag in precipitation hardening of the alloy. The hardness and strength of the Ag–containing alloy were increased by more than 10% due to a higher number density of fine aggregates, which was 2.5 times that of the Ag–free alloy 7075. Both T–type and η–type precipitates existed in the alloys, and two precipitation sequences occurred simultaneously as: SSS → η–type cluster → GP zone → η′ → η → T, and SSS → T–type cluster → GP zone→ T′ → T. Particularly, Ag promoted the formation of T–type clusters due to the interaction among Ag, Mg and Zn atoms as well as vacancies at the early stage of aging. The Mg–Ag, Zn–Ag, and vacancy–Ag co–clusters acted as nucleation sites for the subsequent precipitates (η′, T′, etc.). This also caused the increase of Mg concentration in T–type clusters at the beginning of aging and the narrowing of the precipitation free zone (PFZ) near grain boundaries at the peak aging.