Alptekin Kisasoz

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.

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.

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.

Finite Element Analysis of 2205 Duplex Stainless Steel Welds

Abstract Duplex stainless steels are sensitive to high temperature exposure. The microstructure of the duplex stainless steels changes at high process temperatures. Such microstructural changes might affect the mechanical properties and corrosion resistance of duplex stainless steel. Therefore, the microstructural properties of 2205 duplex stainless steel welds were studied and respective microstructural changes during the welding process have been investigated by finite element analysis before fabrication process. 2205 duplex stainless steels were welded using the TIG process. The heat distribution along the cross section of weldments according to the TIG welding parameters was calculated by finite element analysis using ANSYS software. After metallographic preparation of the weldments, each sample was etched by electro-chemical method and the ferrite-austenite ratio was examined by light microscopy. The finite element analyses and microscopic results were compared and the mechanical properties of the weldments were investigated using hardness tests.

The fabrication and characterization of Al/SiC-MMC castings produced by vacuum assisted solidmould investment casting process

In this paper, a promising manufacturing approach to cast metal matrix composites is proposed. In order to produce metal matrix composites by investment casting, SiC preforms were fabricated in 3D structure. Afterwards, A6063 aluminium alloy matrix material was infiltrated into preforms which were placed in the solid investment casting moulds with vacuum assistance. Preforms were characterized using Archimedes’ test, scanning electron microscope ana X-ray diffraction analysis. Also, fabricated cast specimens, were characterized using hardness tests, image analysis and scanning electron microscope observations. The results show that, in the vacuum assisted solidmould investment casting method; infiltration, of the preforms by molten metal was successfully achieved. Moreover, hardness of the composite higher than the matrix up to ratio of 100% by SiC reinforcement and T6 heat treatment.

Characterization of Mechanical Properties and Corrosion Behaviours of Mn and Al Bronze Castings

Abstract From ancient times to the present, copper alloys, brasses and bronzes are used for marine applications due to their high resistance to sea water. In time, numerous of copper alloys have been developed and manganese (Mn) and aluminium (Al) bronzes are the well-known members of this large family. They have superior properties and are used to produce some critical components of boats. These alloys are in competition with each other. For this reason, C86500 Mn bronze and C95800 Al bronze were evaluated in this study. Mechanical and corrosion tests were carried out on specimens which were taken from sand castings. Tensile, impact and hardness tests were applied to determine mechanical properties. Corrosion behaviour of the alloys was characterized in HCl, NaCl, and H2SO4 solutions. Additionally, microstructure observations and a definition of phases were realized. According to mechanical tests results, Al bronze has better properties than Mn bronze. Moreover, Mn bronze provides lower corrosion rates in HCl solution as Al bronze in H2SO4. Intergranular corrosion was detected in HCl solutions. Moreover, some micro shrinkage zones were seen on an Al bronze specimen after corrosion tests.

Corrosion behavior of alloy AA6063-T4 in HCl and NaOH solutions

Abstract AA6XXX aluminum alloys are widely used in the automotive and aeronautic industries and for food packaging thanks to their lightness, specific strength, and corrosion resistance. The mechanical properties of AA6XXX alloy increase through an age hardening process thanks to the formation of Mg2Si particulates. These particulates enhance mechanical strength and likewise change corrosion resistance. In this study, the corrosion behavior of AA6063-T4 alloy in acidic and alkaline media was investigated and the results were compared with AA6063-T651 alloy. Acidic media was prepared in a 0.1M HCl solution; alkaline media was prepared in a 0.1M NaOH solution. Corrosion tests were performed for 360 hours in both solutions. Corrosion properties were determined by measuring weight loss and surface roughness values of the samples and pH values of the solutions. In both environments, artificially aged samples were found to have higher corrosion rates. There was a direct relationship between corrosion loss and surface roughness values.

Influence of orbital shaking on microstructure and mechanical properties of A380 aluminium alloy produced by lost foam casting

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 changing the dendritic structure into globular. Accordingly increasing in density and mechanical properties were reported. In this work, orbital shaking technique was used alternatively to conventional mechanical vibration in lost foam casting (LFC) of A380 aluminium alloy. In the experiment castings, effects of shaking movement and speed during pouring were investigated. First of all orbital shaking movement has not damage LFC parts and any shape disorder was not occurred. Optical microstructure observations show that, the increase in shaking speed, decrease secondary dendrite arm spacing (SDAS) and partial dendrite arm fractures were determined at 150 rpm shaking. Density and hardness of as cast specimens were increased with shaking and rising shaking speed as well.

Investigation of spherisation in microstructures of aluminium casting alloys for thixoforging process

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 of further semi-solid process. Al-Si alloys are still castable even at low temperatures due to their excellent fluidities. This study subjects to present spherisation of A356 and A380 alloy billets cast with LSC process that provides appropriate beginning material with relatively high sphericity. Obtained billet parts were reheated for different times at a semi-solid state temperature. Some of these billets were directly quenched for observing the effects of reheating and the others were thixoforged. With sufficient reheating time, deformation of thixoforging process did not significantly affect on the spherical microstructure. Unnecessarily long reheating period caused excessive grain growth. A356 alloy had higher spherisation tendency than A380 alloy under similar process conditions.