Yavuz Sun

Wear Behaviors of AA 6063 Aluminum Alloys Reinforced with in situ Al3Ti Particles

The purpose of this study was to examine the microstructure and room temperature dry sliding wear performance of AA 6063 aluminum alloys containing up to 2% Ti under homogenized and heat-treated conditions. After casting, homogenizing heat treatment was applied to all produced alloys at 500°C for 2 h. Heat treatment included water quenching after being kept at 500°C for 2 h, and then an aging process was applied at four hour intervals up to 48 hours, at 150°C. The microstructure of the homogenized and aged alloys was analyzed using a scanning electron microscope (SEM). Hardness measurements were carried out using a microhardness test. Wear tests were performed using a ball-on-disc method by measuring the wear scar areas. Results of the wear tests proved that the wear rate decreased in alloys containing Ti. Though aging heat treatment improved the wear resistance of Ti-free alloys, the wear resistance of each of the alloys containing Ti decreased.

Characterization and Reduction Behavior of Cold-Bonded Composite Pellets for Direct Reduction Using an Organic Binder

The purpose of this study was to investigate the reduction behavior of cold-bonded composite pellets produced from low-grade hematite iron ore using molasses solution at various concentrations, as well as their physical and chemical properties. Direct-Reduction Iron (DRI) technology makes it possible to assess low-grade iron ores and convert them into scrap at facilities that have electric arc furnaces. The reductant used was coke with fixed carbon of 86.04%. The alkalinity rate was adjusted to 0.7 by adding calcium carbonate. In the composite pellets produced, the 300 N/pellet compression strength recommended in the literature was achieved with a Fetot/Cfix ratio of 2.5 and 3 using a 50% concentrated molasses solution. Composite pellets prepared with a Fetot/Cfix ratio of 3.5 using a 40% concentrated molasses solution reached a compression strength of 496 N/pellet. The porosity is inversely proportional to the increase in compression strength and binder concentration. Reduction experiments were conducted by applying different temperatures and durations to samples possessing optimum conditions for each Fetot/Cfix ratio: the best result was achieved with a 88% reduction rate in composite pellets with a Fetot/Cfix ratio of 3.5 at the end of 1 h. Pig iron nuggets were characterized using an optical microscopy (LOM) and a scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS).

Mechanical Properties of Pattern Welded 1075-15N20 Steels*

Abstract Forged welded (damascus) steels are produced by traditional methods and mostly used in the design of decorative tools. These steels are well-known for their good mechanical properties. The process for making forged welded (damascus) steel consists of stacking alternating sheets of different kinds of steel on top of each other and then forge welding them together. In this study, the steels 1075 and 15N20 were used for the forging and folding procedure. The effect of fold numbers on the microstructure and mechanical behavior were investigated. The steel consisted of both materials, 54 and 250 layers, respectively, produced by forge welding. The pattern layers are homogeneous and regular, but after the process sections with up to 54 pattern layers were irregular. Steel 1075 has a pearlitic microstructure, while steel 15N20 has a ferritic microstructure. The impact toughness and tensile strength of the folded steels improved with increasing the number of folds.

An investigation on dry sliding wear behaviour of pressure infiltrated AA1050-XMg/B4C composites

Abstract In this study, the effect of Mg alloying addition (1–4 wt.%) on dry sliding wear behaviour of AA1050 matrix composites was investigated. Composites were produced by the pressure infiltration technique at 800°C and had a B4C particle volume fraction of 60%. Reinforcement particles were uniformly distributed in the aluminium matrix. Compared with the AA1050 matrix, the weight loss of the composites decreased with increasing Mg content. The wear rate of the composites increased when the applied load and sliding distance were increased. The results show that when the applied load reaches critical values (30 N), the weight loss increases significantly.

The effect of head hardening process on the residual stress of rails

In this study, the head hardening process was employed, by using a mixture of air and water under laboratory conditions, to improve the residual stress behavior of R260 grade rails . For this purpose, three types of specimens were selected. One group of rails was heated up to the austenite stage and then cooled for 20 s; the next group was heated up to the austenite stage and then cooled for 40 s and the third group was not exposed to any heat treatment. The hardness results showed that the specimens cooled for 40 s had excessive hardness; the specimens cooled for 20 s exhibited similar properties as that of R350HT rail standards, which are especially preferred in the lower radius of curvature bends in railways, but not that of R260. According to the analysis of residual stress, all samples had compressive residual stress, but the specimens cooled for 20 s had the highest stress value.

Influence of multi-wall carbon nanotube content on dry and corrosive wear performances of pure magnesium:

The present study aims to investigate the effect of Multi-Wall Carbon Nanotube on dry sliding and corrosive wear performance of pure magnesium. Multi-wall carbon nanotube reinforced composites with different weight fractions (0.25 wt.% and 0.5 wt.%) were fabricated by semi powder metallurgy. Hardness test was performed for all samples. To evaluate wear performance of the samples, three different loads (10 N, 20 N, and 40 N) were applied at the room temperature in both dry and 3.5 wt.% NaCl corrosive environments. Worn surfaces and microstructures of the samples were characterized using Scanning Electron Microscope. Results show that carbon nanotubes embedded in the matrix without any macro-defects. The hardness of pure magnesium was improved with the addition of multi-wall carbon nanotube considerably. 0.5 wt.% multi-wall carbon nanotube reinforced composite exhibited best wear performance both in dry and corrosive conditions.

Investigation of wear behaviour and microstructure of hot-pressed TiB2 particulate-reinforced magnesium matrix composites

ABSTRACT In this study, magnesium and magnesium metal matrix composites (Mg-MMCs) reinforced with 10, 20 and 30 weight (wt.)% TiB2 particulates were produced by powder metallurgy using the hot pressing technique. The hardness, density, wear behaviour and microstructure of samples were investigated. Uniform distributions of TiB2 particulates were observed except with some partial agglomeration for 30 wt-% TiB2. When compared to pure Mg, the hardness increment of Mg-MMCs reinforced with 10, 20 and 30 wt-%TiB2 particulates was 10.7, 31.9 and 65.3%, respectively. As compared to pure Mg, under load of 20 N, the decrease in wear rate in 10, 20 and 30 wt-% reinforcement was 28.71, 34.98 and 42.92%, respectively. It is believed that the reason of decrease in wear rate was the presence of harder TiB2 particulates, which resisted to wear and plastic deformation. For pure Mg, oxidative wear changed to oxidative and mild abrasive wear transition from 10 to 20 N. Mg/TiB2 composites exhibited abrasive wear mechanism under load of 10 and 20 N except 30 wt-% TiB2 composite indicated oxidative and adhesive wear. However, a transition from mild abrasive wear to severe abrasive wear was observed with increasing load in composites.

Microstructure and corrosion properties of lanthanum-added AZ31 Mg alloys

In this study, the effect of lanthanum (La) on microstructure and corrosion properties of hot-rolled AZ31 Mg alloys was investigated. Light optical microscopy, scanning electron microscopy, and X-ray diffraction were applied for microstructure analysis. Potentiodynamic corrosion and immersion tests were being tried to assess the La effect on corrosion behavior. Moreover, how the rolling parameters and surface smoothness were changed of the corrosion rate was evaluated. Corrosion performance was developed by adding La and the corrosion rate was changed with the rolling speed.

Effect of Sn Addition on Corrosion Properties of As-Cast and Hot-Rolled AZ31 Magnesium Alloys

This study investigates the effect of Ti addition (0, 0.2, 0.5, 1wt%) on corrosion resistance of as-cast and hot rolled AM60 magnesium alloy. Corrosion behaviors were investigated by immersion tests and electrochemical analysis. The results showed that Ti addition altered the microstructure of as-cast AM60 magnesium alloy by decreasing the amount of β-Mg17Al12 eutectic phase. Homogenization treatment resulted in the dissolution of the most of the β-Mg17Al12 phases. Homogenized samples exhibited the lowest corrosion rate in immersion test while the best corrosion resistance was found for hot-rolled samples in electrochemical test. In hot-rolled state, Ti addition led to a slight change in the corrosion resistance of AM60 magnesium alloy.

Microstructure and Corrosion Properties of Homogenized Mg-4Zn-1La Magnesium Alloy

In this study, microstructure and corrosion behaviour of homogenized Mg-4Zn-1La magnesium alloy was investigated. Mg-4Zn-1La alloy was produced by low-pressure die casting method. Homogenization treatments were performed at 350 °C and 400 °C for 12, 18, 24 and 48 hours, followed by rapid cooling in water at room temperature. Microstructure characterizations showed that La addition led to a formation of semi-continuous network structure and islands of second phases which identified as T-phase (Mg7Zn3RE). A significant amount of second phase dissolution and an increase in a-Mg grain size with increasing both homogenization time and temperature was observed. Homogenization treatment led to an improvement in corrosion resistance of Mg-4Zn-1La alloy. Homogenization at 400 °C resulted in better corrosion resistance than homogenization at 350 °C for all homogenization duration.