Ahmet Durgutlu

A novel approach to diffusion bonding of copper to stainless steel

In this study, austenitic stainless steel and copper materials were bonded through the diffusion welding method, one of the solid-state welding processes. The welding process was carried out at 875°C temperature for 30 minutes under 3 MPa pressure. Two different methods were employed in the welding process. In the first method, the conventional diffusion welding procedure was followed. In the second one, an external electrical current was applied to the parts to be joined with the help of a system that was added to the conventional system. By doing so, the aim was to determine the diffusion amount and length for the specimens obtained with and without current. The weld quality of the diffusion welded specimens was examined using the tensile and hardness test. In addition, microstructural analyses were done using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The highest hardness value was obtained in regions next to the interface and it was decreased gradually as the distance from the interface increased on both sides of the interface. The results indicated that the highest interface strength was obtained for the specimens joined when the external current was applied. According to the EDS and EDS line element analyses results, it can be seen that the specimens joined by applying the external current had a higher amount of diffusion and length than the specimens joined by the conventional technique.

Investigation of the Microstructural, Mechanical and Corrosion Properties of Grade A Ship Steel-Duplex Stainless Steel Composites Produced via Explosive Welding

AbstractGrade A ship-building steel-AISI 2304 duplex stainless steel composite plates were manufactured via explosive welding. The AISI 2304 plates were used to clad the Grade A plates. Optical microscopy studies were conducted on the joining interface for characterization of the manufactured composite plates. Notch impact, tensile-shear, microhardness, bending and twisting tests were carried out to determine the mechanical properties of the composites. In addition, the surfaces of fractured samples were examined by scanning electron microscopy (SEM), and neutral salt spray (NSS) and potentiodynamic polarization tests were performed to examine corrosion behavior. Near the explosion zone, the interface was completely flat, but became wavy as the distance from the explosion zone increased. The notch impact tests indicated that the impact strength of the composites decreased with increasing distance from the explosion zone. The SEM studies detected brittle behavior below the impact transition temperature and ductile behavior above this temperature. Microhardness tests revealed that the hardness values increased with increasing distance from the explosion zone and mechanical tests showed that no visible cracking or separation had occurred on the joining interface. The NSS and potentiodynamic polarization tests determined that the AISI 2304 exhibited higher corrosion resistance than the Grade A steel.

Patlama Kaynağı Yöntemi ile Birleştirilen Östenitik Paslanmaz Çelik (AISI 316L) – S235JR Kompozit Malzemelerde Patlayıcı Oranının Mikroyapı ve Yorulma Özelliklerine Etkisi

Bu calismada, ostenitik paslanmaz celik (AISI 316L) ve S235JR levhalar, kati hal kaynak yontemlerinden olan patlama kaynak yontemiyle iki farkli patlayici orani (R=1.5-2) kullanilarak birlestirilmistir. Elde edilen kompozit malzemelerin birlesme arayuzeylerinde meydana gelen degisimleri gormek ve mekanik ozelliklerini tespit etmek amaciyla mikroyapi, sertlik ve yorulma deneyleri gerceklestirilmistir. Deneyler sonucunda dusuk patlayici oraninin kullanildigi numunelerin birlesme arayuzeyinde olusan dalgalanmanin cok dusuk boyutlarda oldugu gorulmustur. Daha yuksek patlayici oraninin kullanildigi numunede ise artan patlayici orani ile beraber arayuzeyde olusan dalgalarin boylarinda ve genliklerinde bir artis meydana geldigi tespit edilmistir. Patlayici oraninin artmasiyla beraber olusan deformasyondan dolayi kompoziti meydana getiren malzemelerin sertliklerinde de bir artisin meydana geldigi belirlenmistir. Kompozit malzemelere uygulanan yorulma deneylerinde ise patlayici oraninin artmasiyla beraber kompozitlerin yorulma omurlerinde bir azalmanin meydana geldigi tespit edilmistir.

The Effects Of Critical Welding Parameters On Tensile-Shear Properties Of Friction Stir Spot Welded Polyethylene

The aim of this study was to investigate the weldability of high density polyethylene via friction stir spot welding method. Polyethylene sheets were joined with dwell times of 60 to 100 s, three different pin profiles (M6×1, M6×1.25, M6×1.5) and pin lengths of 3.75 to 4.75 mm by using rotational speed of 900 rpm and delay time of 45 s. During welding processes, the temperatures were measured under the welding centers. The tensile-shear tests were performed to welded samples. Also, macrostructures of welding nuggets were examined. The small welding nuggets were formed by using the lower dwell time. The melting in welding nugget occurred in the all dwell times during the welding. The dwell time affected on the friction temperature. The key (pin) hole closed when sufficient friction temperature (dwell times of 80 and 100 s). The pin profiles directly affected the welding quality. Large screw pitch range of the pin and the small pin length from 4.5 mm negatively affected the weld fracture load. Pin length of the stirring tool directly affected the quality of welding.

The effect of continuous and pulsed current on microstructure and mechanical properties in TIG welding of Al-Si alloy sheets

In this experimental study, Al-Si alloy sheets were joined through TIG welding method by using continuous current and pulsed current. Tensile test, bending test, hardness test, and microstructure examination of joined test samples were carried out in order to see the effect of current type on mechanical properties of welded samples. Experimental results showed that pulsed current led to low heat input, grain refinement, and hardness increase in weld metal compared to alternative current. The samples joined by using the pulsed current showed higher tensile strength than the samples welded by using the alternative current. After bending test, cracks, tearing, and surface defection were not observed in the samples. K e y w o r d s: aluminium, TIG welding, current type, mechanical properties

Effect of Continuous and Pulsed Currents on Microstructural Evolution of Stainless Steel Joined by TIG Welding

Abstract In this study, AISI 316L series austenitic stainless steel sheets were joined by tungsten inert gas welding method in continuous and pulsed currents. Regarding microstructural investigation and hardness values of weld metal, samples were welded to investigate the effect of current type on grain structures of weld metal. Results showed that samples welded by using pulsed current had considerable different properties compared to the samples welded by using continuous current. While the weld metals of joinings obtained by using continuous current displayed a coarse-grained and columnar structure, weld metals obtained by using pulsed current had a finer-grained structure. It was also found that hardness values of samples, which were welded with continuous and pulsed current, were quite different.

An Investigation of TIG Welding of AZ31 Magnesium Alloy Sheets

Abstract In this study, butt welding of commercial AZ31 magnesium alloy sheets has been investigated by using the tungsten inert gas welding process with alternating and pulsed current. Magnesium alloy welding, although well developed and understood, can present some problems, such as porosity, hot cracking, oxide formation, etc. Samples of the welded parts have been examined by optic microscopy and mechanic tests. Results showed that porosities and homogeneous micro size oxides were rarely found. Orientation of the weld microstructure in direction of the heat transfer were also rarely observed and equiaxed grain morphology was the dominant grain structure as in the base metals. In addition, fusion zone and HAZ of the welded samples have generally shown twins. This seems to be a very dominant grain type particularly in pulsed samples. Hot cracking was not observed in any samples. Results of mechanical tests showed that pulsed current seems to generate more favorable higher mechanical properties of weld joints than alternating current for magnesium alloys.

INVESTIGATION OF THE MECHANICAL PROPERTIES OF DIFFERENT THICKNESS OF THE GRADE A SHIP PLATES JOINED BY SUBMERGED ARC WELDING

In this study, a large part of the ship used in the manufacture of three different thickness of Grade A ship plates were joined by submerged arc welding method. In order to determine the strength of welded joints to the tensile and charpy impact test were applied, as well as hardness and microstructure studies were conducted on samples. Tensile tests showed that rupture occurred in the base metal of all samples. From the results of charpy impact test, the highest charpy notch values were obtained from base metal and this is followed by HAZ and the weld metal. It was seen that all the welding parameters, weld metal hardness is higher than the HAZ and the base metal.

Microstructural Evolution and Weldability of AISI 4042 Steel

High carbon content and addition of other elements, such as Mn in steel, causes some difficulties in the weldability of these materials. In this study, pre and post heating processes were applied for the multipass welded specimens. Tensile test, notch impact test and hardness measurements were carried out, and microstructural features were examined. The weldability of these steels can be improved with the pre and post heat treatments. Maximum hardness values were obtained for the non-heat treated specimens due to large grain structure and high volume percentage of the pearlite content. Although applied heat treatments caused decrease in hardness values, an increase in tensile properties and toughness values at all temperatures occurred. Changes in these properties were explained in the light of the microstructure of the AISI 4042 steel specimens.