Ahmet Karaaslan

Fabrication of Al/Mg Bimetal Compound Casting by Lost Foam Technique and Liquid-Solid Process

Abstract In the present experimental study, bimetal aluminium/magnesium macro composites which contain magnesium core were fabricated via compound casting by lost foam casting process. AM50 Mg alloy prismatic core was placed into a cubic EPS foam pattern. Conventional process steps of lost foam casting were followed and A319 casting aluminium alloy was melted and poured. Experimental studies have shown that determination of casting temperature is very important to avoid melting of Mg alloy core. Microstructures of sectioned cast specimens were observed by light microscope and scanning electron microscope (SEM). Energy dispersive X-ray spectroscopy (EDS) analysis and Brinell hardness tests were carried out. Especially, transition zone and Al/Mg interface were in the focus of research.

A novel method for Al/SiC composite fabrication: Lost foam casting

Abstract In this paper, an innovative manufacturing approach to cast metal-matrix composite is proposed. Aluminum matrix composite production by lost foam casting has been investigated. In order to produce metal-matrix composite by lost foam casting, expanded polystyrene boards were designed as sandwich shaped and three layered. SiC particulates with 60 lm average grain size were settled between the board layers, while A6063 and A413 aluminum alloys were used as matrix materials. The effect of the matrix materials on the mechanical properties of the composite specimens was investigated and fabricated specimens were characterized using image analysis, hardness tests, scanning electron microscope and X-ray diffraction analysis. The results show that in the lost foam casting method, the hardness of the A6063 and the A413 materials specimens increases with SiC reinforcement up to 70% and 80%, respectively.

Effects of pattern coating and vacuum assistance on porosity of aluminium lost foam castings

Lost foam casting (LFC) process has several advantages when compared to conventional sand casting techniques however formation of large amount of gaseous products during foam pattern removal increases porosity fraction of castings, especially for low melting point A1 and Mg alloys. In this study pattern coating and vacuum assistance at the time of filling were investigated and their characterizations in constant casting conditions have been determined. Green sand moulding technique was carried out for all moulds because it is necessary to obtain sound castings by using expandable polystyrene (EPS) foam patterns without refractory coating. Simple prismatic shaped patterns were prepared from cutting pieces from an EPS isolation board. A well-known A380 Al-Si-Cu casting alloy was cast at 730°C. As expected, pattern coating reduce the gas permeability and increase porosity however metal penetration into sand grains and surface roughening occurs without coating. Slight vacuum were applied to moulds with vacuum casting machine until solidification. Vacuum assistance enhanced gas removal and it has clear effect on decreasing porosity.

The Effect of RRA Heat Treatment on the Intergranular Corrosion (IGC) of the AA7075 Alloy

Abstract 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 the alloy to IGC was determined by weight loss detection, macro and microstructure studies. Scanning electron microscope (SEM) analysis was also performed. According to the results obtained, it was determined that the RRA processes in the AA7075 alloy change the grain boundary morphology and decrease the IGC corrosion susceptibility.

A study of expanded polyethylene (EPE) pattern application in aluminium lost foam casting

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 applications of other kind of foams, expanded polystyrene (EPS) is the most common pattern material of LFC process. It has been used since onset of the method. In this work, expanded polyethylene (EPE) was used as alternative pattern material and compare with EPS by aluminium castings in two different temperatures. Casting experiments were carried out with a well known aluminium alloy A380 at 720°C and 780°C. Porosity contents of the specimens were investigated and compared with density calculations and stereo microscope observations. In brief, EPE can be an alternative pattern material only in right conditions and it is not as useful as EPS. It slows down metal flow and in low casting temperatures EPE causes misrun. Also its decomposition residues contaminate moulding sand.

Fillet welding of austenitic stainless steel using the double channel shielding gas method with cored wire

Abstract X2CrNi189 austenitic stainless steel material with web and flange thicknesses of 10 mm was welded by the conventional GMAW and double channel shielding gas method to form double fillet T-joints. The difference between these two methods were characterized by measurements of mean welding parameters, Vickers hardness profiles, molten and HAZ areas of the joints as well as by thermal camera temperature measurements. According to the results, higher mean current intensity but lower mean arc voltage along with higher heat input was obtained using the double channel shielding gas method. There was no significant difference observed in Vickers hardness between the two methods. Moreover, mean filler metal molten area values were higher with double channel shielding gas method, which depicted that this method increased productivity.

Mechanical and Microstructural Evaluation of DMAG Welding of Structural Steel

Double channel torch, which allows concentric flow of two different shielding gases, was designed and manufactured in order to pursue double channel torch gas metal arc welding of unalloyed structural steel S235JR (EN 10025-2) with fourteen passes. Tensile and Charpy V-notch tests were realized and the results were compared with those of conventional gas metal arc welding. In order to evaluate mechanical testing results, microstructural analyses were conducted. It was found that the increase with double channel gas metal arc welding process in yield and tensile strengths as well as in toughness tests, especially in subzero temperatures, compared with conventional gas metal arc welding was due to longer columnar grains and finer tempered zone grain structure between passes and due to solidification and less dendritic structure formation in all-weld metal in double channel gas metal arc welding.

Tensile Strength and Impact Toughness of an AA 7075-T6 Alloy

Abstract In this study retrogression and aging treatment have been applied to the samples of an aluminum alloy AA 7075-T6. The retrogression treatment has been performed with different temperatures and times and then aging treatment has been applied at 130°C for 12 h. By determining the effects of the retrogression treatment temperatures and times on the samples, the microstructral and also mechanical changes in AA 7075-T6 alloy have been examined. All microstructures have been investigated by Scanning Electron Microscopy (SEM). Additionally, the mechanical properties have been determined by the notched impact test and the tensile test.

Effect of Annealing Time and Cooling Rate on Precipitation Processes in a Duplex Corrosion-Resistant Steel

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.

Evaluation of double channel GMAW fillet welds of low carbon steel using solid wire

Abstract 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 thermal camera temperature measurements. According to the results, lower mean arc voltage along with lower heat input was obtained using double channel shielding gas method. Vickers hardness values were higher using conventional GMAW. Moreover, mean filler metal molten area values were higher using double channel shielding gas method, which depicted that this method increased productivity. Smaller HAZ area values acquired with double channel shielding gas method is an indication of more intense heat input.