Ahmet Karaaslan

Yildiz Technical University · Department of Metallurgical and Materials Engineering

Ni-based G-NiCr28W alloy, which is widely preferred in high-temperature applications, has an austenite matrix as well as carbides dispersed in the structure. The morphology of the carbides in the structure varies depending on the chemical composition and heat treatment. Carbide phases commonly seen in these alloys are MC, M7C3, and M23C6. These car...

304 stainless steel (SS)/A356 aluminum bimetal composites were manufactured by vacuum-assisted melt infiltration casting successfully. SS chips with different volume fractions of 35%, 50%, 60%, and 65% were used in a composite structure. Low-cost, environmentally friendly production was achieved by using chips as reinforcing material. Dry sliding b...

Gas tungsten arc welding is a preferred welding process due to its excellent heat control which provides high quality joinings of various metals. Welded armor steels are widely used in armored vehicles for the ease of production. Thus, characterization of gas tungsten arc welding of armor steels reveals important data on both present applications a...

Inconel 625 alloy is used in aggressive environments at high temperatures such as in petro-chemical applications, in the aeronautical and nuclear energy industries because of its propitious mechanical properties and corrosion resistance. In this study, Inconel 625 samples were joined with ERNiCrMo-3 filler metal using the MIG (metal inert gas) meth...

In this paper, retrogression and re-aging (RRA) heat treatment was applied to 7075 aluminum alloy in T6 condition at different times (30 and 90[Formula: see text]min) and temperatures (180 ∘ C and 240 ∘ C). While RRA heat treatments increase the corrosion resistance of the material, it does not harm its mechanical properties. On the other hand, the...

In this study, AA7075 aluminum matrix composites reinforced with the combination of SiC, Al2O3, and B4C particles were fabricated by the liquid metal infiltration method. The effects of the relative ratio of B4C and Al2O3 particles on the microstructural, wear, and corrosion features of the composite samples were analyzed using XRD, light metal mic...

In this study, the effect of multipass welding on the microstructure, mechanical and corrosion properties of the UNS 32205 duplex stainless steels (DSS) is investigated. The UNS 32205 DSS is welded in 3 or 7 passes by flux-cored arc welding (FCAW) using E2209 T1 – 1/4 flux cored wire. The weldments are characterized by light optical microscopy (LOM...

Metal matrix composites have a wide range of applications due to their lightweight, high strength and high wear resistance. In this study, Al2O3-reinforced AA7075 matrix composites were produced by using liquid metal infiltration method in two stages. In the first stage of the production, preforms were manufactured by using Al2O3 particles and diff...

A Micro arc oxidation coatings were produced on AA7075 (UNS A97075) sub-strates using various process parameters. The study aimed to improve the surface characteristics of the alloy. Thickness, hardness, and roughness measurements characterized the coatings. It was revealed that the coating thickness was directly related to the coating roughness. V...

In this study, direct aging (aged‐490 °C/6h) and solution heat treatment and subsequent aging (SHT‐940 °C/2h + 490 °C/6h) heat treatments were applied to Maraging Steel (MS1) produced by Direct Laser Metal Laser Sintering (DMLS) method. The effects of these heat treatments on microstructure, phase transformations, mechanical properties, and corrosi...

This study aims to determine optimum casting temperature to achieve maximum wear and corrosion resistance in 304 stainless steel (SS) reinforced A356 matrix bimetal composites, which have been developed for use where conventional ceramic reinforced metal matrix composites have been used. Vacuum-assisted melt infiltration casting technique was used...

In this study, numerical modelling was applied in order to determine the conductivity values of AA1050, AA3005, AA3104, and AA3105 alloys after different thermomechanical processes. Conductivity difference contour plot graphs of aluminum were performed with different thermomechanical processes. Samples were taken from AA1050, AA3005, AA3104, and AA...

Cooling slope casting has been applied to aluminium casting alloys for producing ingots with non-dendritic microstructure. Semi-solid forming of the AA7075 was studied via cooling slope casting, reheating and thixoforging processes in order to determine the effect of semi-solid casting on the microstructure of the alloy. AA7075 ingots with non-dend...

In this study, effect of cooling rate on the microstructure and corrosion behavior of the solution-treated 1.4462 alloy was investigated. 1.4462 alloy was heat-treated at 1000 °C, 1120 °C and 1200 °C for different duration in order to obtain various phase balance. Two different cooling regimes (rapid cooling and steady cooling) were applied followi...

Aluminium matrix composites which are the most widely used in metal matrix composites have a wide range of use in the aerospace and automotive industry due to their superior properties such as high specific strength, chemical stability, high wear resistance and low density. In order to increase the desired mechanical properties in metal matrix comp...

AA7075 matrix bimetal composites reinforced with 304 stainless steel (SS) were manufactured by melt infiltration casting technique. A preform, made by assembling 304 SS shavings under 220 MPa pressure, was infiltrated by molten AA7075 alloy under vacuum atmosphere during this process. The preform was preheated for 10 min before infiltration to avoi...

AA6063 was heat treated with different retrogression temperatures and durations, and the effect of heat treatment conditions on the microstructure, hardness, electrical conductivity, intergranular corrosion (IGC) and electrochemical corrosion behaviours of the AA6063 was determined compared with the T6 condition. The IGC test was applied according...

The automotive industry needs the combination of lightweight and high-strength materials which can be achieved by using aluminum matrix composites (AMCs). Production problems and expensiveness of conventional ceramic reinforced AMCs can be overcome by the use of metals as reinforcements. This study intends to demonstrate the potential of commercial...

In this study, a retrogression process (R) has been applied to AA7075 at 180, 240, and 370°C for 15, 30, 90, and 120 min. After the retrogression, reaging treatment (RA) was reapplied with T6 conditions (120°C for 24 hr). The effect of different temperatures and time periods of retrogression and reaging temper on exfoliation corrosion (EXCO) of the...

The unresolved production problems including wettability and undesired intermetallic phase formation at the interface of aluminium matrix composites (AMCs) with ceramic reinforcements require a different approach to the subject. Titanium as a reinforcement is a strong candidate to overcome the current problems, without sacrificing beneficial featur...

The effects of different retrogression times and temperatures on the microstructure, electrical conductivity, exfoliation corrosion (EXCO), and hardness of the 7050 aluminium alloy were compared with the T6 and T7451 condition. The EXCO solution was prepared in accordance with ASTM G34‐01 standard and the samples were kept in the solution for 48 hr...

This study aims to investigate the effect of volume fraction of commercially pure titanium (CP-Ti) on microstructural, mechanical, and tribological features of A356 aluminum matrix composites. Vacuum-assisted melt infiltration casting was performed to produce composites with 50%, 65%, 75%, and 80% CP-Ti contents. CP-Ti sawdusts were assembled under...

This study aims to identify the optimal burnout temperature (BT) of a plaster mold that was used in bimetal composite production. To achieve this goal, the mold was gradually heated up to 600, 650, 700, and 750 °C prior to melt infiltration casting. Molten A356 aluminum alloy was cast into mold at 730 °C for each casting process. Fifty percent poro...

A356 aluminium alloy/commercially pure (CP) copper bimetal was produced via liquid-solid process by lost foam casting (LFC) technique. Cu rod was placed into an expanded polystyrene (EPS) pattern followed by applying thermoplastic adhesive to cover apertures between rod and foam, pattern coating, drying and moulding in a steel flask using free sili...

Gallium doped zinc oxide (ZnO:Ga) thin films were deposited on glass substrates by means of r.f. magnetron sputtering at room temperature, non-reactively. Both the wet chemical etching behavior and the influence of etching time variations on ZnO:Ga films were investigated. 0.1 % HCl was used as an etchant and the etching time varied in small increm...

In this study, the effect of commercially pure Ti volume fraction on the properties of Al-Ti bimetal composites manufactured by using CP-Ti sawdusts which allow environmentally friendly and low cost production was investigated. For this purpose, CP-Ti sawdusts were assembled under 110, 220, 330 and 440 MPa pressures and monoblock preforms including...

Duplex stainless steels (DSSs) have ferrite and austenite phases in equal amount. Ferrite and austenite phases are balanced in the microstructure by solution treatment (ST) applied above 1000°C. The decent mechanical features of DSSs are achieved by combining the individual properties of ferrite and austenite phases after ST. Cooling condition afte...

Automotive industry requires lightweight structures considering fuel economy, vehicle safety and emission reduction concerns. Aluminium matrix composites (AMCs) have been widely used in automobile components such as cylinder heads, engine pistons or disc rotor brakes due to their high strength/density ratio and excellent wear resistance. Generally,...

304 stainless steel (SS) and commercially pure titanium (CP-Ti) reinforced AA7075 aluminum matrix hybrid composites were manufactured by melt infiltration casting under vacuum atmosphere. Various SS and CP-Ti contents (at the ratios of 3:1, 1:1 and 1:3) in AA7075 alloy were studied and the effects of SS/CP-Ti ratio on wear resistance of produced co...

In this research microstructural variations for A356 aluminum casting alloy were examined with different casting methods and different solution heat treatment time. Permanent and green sand moulds were used for casting processes which were carried out at 730°C. Effects of different cooling rate which arised from different mould type, and solution h...

Commercially pure titanium (CP-Ti) reinforced A356 aluminum matrix composites were fabricated by melt infiltration casting. Nearly same sized CP-Ti sawdusts were assembled under 440 MPa pressure to procure one-piece preforms with 20% porosity. The vacancies of the preforms were filled by molten A356 alloy in a plaster mould at 700°C under 10-5 Pa v...

The effects of T6 heat treatment on thixoforged A356 and A380 aluminium alloys were studied. Low superheat casting (LSC) technique was carried out to prepare proper specimens for thixoforging process. The samples were poured at 20 °C above their liquidus temperatures which provided the formation of equiaxed grains instead of dendritic growth. Produ...

304 Stainless steel (SS)-reinforced A356 aluminium matrix composites were manufactured by melt infiltration casting. Recycled SS shavings were pressed to obtain porous monoblock preform, and molten Al alloy was infiltrated into vacancies of the preform during casting process. Various preform preheating times (0–60 min) before casting were studied,...

A retrogression process was applied to AA7075 alloy at 180, 240 and 320 °C for 1, 30, 50, 70, 90 and 120 min. After the retrogression, aging treatment was reapplied with T6 conditions (120 °C, 24 h). The mechanical properties of aged samples were determined by V-Charpy and hardness tests and also, physical properties of samples were determined by e...

Thixoforging combined with low superheat casting (LSC) is a promising shaping process for aluminium casting alloys. LSC process is based on rapid solidification of an alloy which cast with low pouring temperature. With this method, a feedstock material is produced with non-dendritic microstructure that ready for spherisation in reheating sequence o...

AA7075 alloys susceptibility to exfoliation corrosion is related to distribution and size of precipitate within grain boundary, continuity within grain boundary and electrochemical behaviour. Distribution and size of precipitate in the grain also effects the conductivity of the material. The effect of different temperatures and time periods of RRA...

The effect of preform preheating on wear behavior of 304 reinforced A356 matrix composite was studied. Stainless steel shavings were pressed to attain porous preforms which were infiltrated by molten A356 alloy in a subsequent process. All casting operations were performed at 730 °C. Preforms were inserted into mould before casting and held for var...

Low carbon steel material and T-joints are frequently used in ship building and steel constructions. Advantages such as high deposition rates, high quality and smooth weld metals and easy automation make cored wires preferable in these industries. In this study, low carbon steel materials with web and flange thicknesses of 6 mm, 8 mm and 10 mm were...

Using vibration for refining microstructure and improve mechanical properties of aluminium alloys castings are in the interest of researchers for many years. Within the framework of these studies mechanical, ultrasonic and electromagnetic vibration applications were carried out. Results of these processes can be summarized as grain refining and cha...

In this study, the effects of retrogression and re-aging (RRA) heat treatment applied on AA7075 aluminum alloy at various times and temperatures on the intergranular corrosion (IGC) behavior were investigated. The IGC solution was prepared according to ASTM G110 – 92 standard and the samples were kept in the solution for 24 hours. Susceptibility of...

In this study, AISI 2205 types of duplex stainless steels were welded by FCAW (flux cored arc welding) using E2209 T1-1/4 type flux cored filler metal. Joinings welded with different heat input and number of passes were characterized by microstructural analysis and charpy impact test. Also, ferrite/austenite phase ratios in welded specimens were in...

Duplex stainless steels (DSSs) have both higher mechanical properties and corrosion resistance in the cause of austenitic and ferritic microstructure. DSSs, generally have equal amount of austenite and ferrite phases. Solution heat treatment is applied to DSSs for providing homogenous microstructure, composing desired austenite-ferrite phase fracti...

The effects of artificial aging on A356 aluminum billets were investigated. Low superheat casting (LSC) was performed in order to prepare appropriate samples by equiaxed grains formation instead of dendrites for further semi-solid metal process. Specimens were cast at 635°C in LSC technique and non-dendritic grains were obtained. Produced billets w...

Nickel based alloys are widely used in high temperature applications because of their decent creep and fatigue strengths. In spite of higher microstructural stability of the Ni-base alloys, physical and microstructural properties are going to change with usage in high temperature applications. In this study, the effect of solution heat treatment at...

Semi-solid metal (SSM) processes have been widely used in aluminum production as an alternative to conventional casting methods for many years. It is possible to obtain uniform non-dendritic microstructure with less porosity by using SSM techniques. Low superheat casting (LSC) is a kind of SSM method that operates at just above the liquidus tempera...

Duplex stainless steels (DSSs) have austenite and ferrite phases in equal amount and DSSs have both higher mechanical properties and corrosion resistance owing to duplex microstructure. In this study, microstructural and mechanical properties of AISI 2205 alloy after solution treatment at 1150˚C1150˚C with various time are investigated. Moreover, t...

This study aims to manufacture aluminum based metal-metal composite (MMC) reinforced with sawdusts which provide strengthening of matrix alloy in an environment-friendly way. Commercially pure titanium (CP-Ti) was used as a reinforcement and A356 aluminum alloy was chosen as a matrix material. CP-Ti sawdusts were compressed in an attempt to obtain...

Semi-solid processes of aluminium alloys have been a focus of interest for many years. Thixoforging is a kind of forging process which is carried out in the semi-solid region of the alloy. Ingots used in thixoforging process cannot be produced by conventional ways; they must be prepared with different processing routes. In this study, low superheat...

Three different etching methods are used to uncover the ferrite-austenite structure and precipitates of secondary phases in stainless steel 22.5% Cr – 5.4% Ni – 3% Mo – 1.3% Mn. The structure is studied under a light microscope. The chemical etching is conducted in a glycerol solution of HNO3, HCl and HF; the electrochemical etching is conducted in...

Thixoforging combined with low superheat casting is a kind of semi-solid technique which is especially used for shaping of aluminium casting alloys. In this work first, ingots were cast in low superheat conditions then they were heat up to semi-solid state and subjected to compression deformation. A380 cylindrical steel die to produce an ingot in d...

Duplex stainless steels which consist of ferrite and austenite phases at almost the same ratio, have high mechanical strength, general corrosion resistance and pitting corrosion resistance owing to existing of ferrite and austenite phases in the microstructure. Duplex stainless steels are widely used in storage tanks, petrochemical industry and mar...

Duplex stainless steels (DSS), including ferrite and austenite phases in the microstructure, are widely used in petrochemical industry, storage tanks and marine applications. Moreover, intermetallic phases nucleate at ferrite-ferrite and ferrite-austenite grain boundaries and grow into ferrite phase when DSS of DSS increases and ductility of DSS de...

This study deals with the production of 7075 aluminum based metal-metal composite using sawdust as reinforcement via vacuum assisted solid mould investment casting. 2205 duplex stainless steel (DSS) and commercially pure (CP) titanium sawdusts were pressed separately in order to make convenient preforms which were infiltrated by molten 7075 aluminu...

X 2 CrNi 18 9 austenitic stainless steel material with web and flange thickness of 6 mm was welded by conventional GMAW and double channel shielding gas method ( DMAG) to form double fillet T-joints. The differences between these two methods were characterized by measurements of mean welding parameters, thermal camera temperature measurements, Vick...

zet Çift fazlı paslanmaz çelikler ferrit ve östenit fazlarını bir arada içeren paslanmaz çeliklerdir. Bu çeliklere yüksek sıcaklıklarda uygulanan işlemler sonucunda ferrit-östenit dengesi bozulmakta ve malzeme özelliklerini olumsuz etkileyen ikincil fazlar oluşmaktadır. Bu çalışmada soğutma ve ısıtma koşullarının mikroyapı özellikleri üzerindeki et...

Soğuk iş takım çelikleri yüksek oranda C içeren, çalışma koşullarında yüksek sertlik ve çok iyi aşınma direnci göstermesi istenen çeliklerdir. Bu tür çeliklerin yapısında yüksek C içeriğinin yanı sıra, Cr, V ve Mo gibi karbür yapıcı alaşım elementleri de bulunmaktadır. Bu çalışmada soğuk iş takım çeliklerinin içerdiği Cr ve V miktarının C miktarına...

The influence of the annealing time after air cooling and cooling with the furnace on the precipitation processes is studied for the SAF 2205(1.4462) duplex corrosion-resistant steel. The kinetics of the precipitation of the intermetallics is determined, and the experimental data are analyzed with the help of the Avrami equation.

S235JR low carbon steel material with web and flange thicknesses of 8 mm was welded by conventional GMAW and double channel shielding gas method to form double fillet T-joints. The differences between these two methods were characterized by measurements of mean welding parameters, Vickers hardness profiles, molten and HAZ areas of the joints and th...

The lost foam casting (LFC) process is a kind of casting technique based on using refractory coated polymeric foam patterns and replacing of them by liquid metal during filling. Except limited applica� tions of other kind of foams, expanded polystyrene (EPS) is the most common pattern material of LFC pro� cess. It has been used since onset of the m...

The wear behavior of cast A7075 and A7075/SAF 2205 composite material fabricated by vacuum-assisted investment flask casting was investigated under dry sliding condition. The wear tests were carried out using a “ball-on-disc” type tribometer. In the wear tests, 100Cr6 and ZrO2 balls were used as counterparts and the load, total distance and rotatin...