Yusuf Ozcatalbas

Investigation of the machinability behaviour of Al4C3 reinforced Al-based composite produced by mechanical alloying technique

Abstract In this study, by the technique of mechanical alloying (MA), aluminium-based composite reinforced contained various amounts of Al 4 C 3 particles, depending on MA time, were produced. The machinability of metal-matrix composites (MMCs) was characterised by the investigation of chip formation, cutting forces and surface roughness. XRD, SEM and mechanical properties of the block samples produced by powder metallurgy technique were investigated. It was found that increasing the duration of mechanical alloying resulted in the formation higher amounts of Al 3 C 4 particles which therefore raised the hardness, but on the contrary decreased the transverse rupture strength of the samples. During the machining of MMCs, elemental and arc chips formation were observed. High volume fraction of Al 4 C 3 in the matrix decreased formation of built-up edge (BUE) and surface roughness at high cutting speeds. Furthermore, it was concluded that the effect of Al 4 C 3 on the crack formation in shear plane, reduced the cutting force, shortened the chip contact length and the chip segment thickness.

Chip and built-up edge formation in the machining of in situ Al4C3–Al composite

Abstract As a consequence of widening range of applications of metal-matrix composites (MMCs), the machining of these materials has become a very important subject for research. This paper describes a study of chip formation during the machining of MMCs produced by the mechanical alloying (MA) technique. Aluminium based composite which contained various amounts of in situ Al 4 C 3 particles, depending on MA time, were produced. Scanning electron microscopy and mechanical properties of the block samples produced by powder metallurgy technique were investigated. The chip-formation mechanism in machining of these MMCs at various cutting speeds has, therefore, been investigated by using a quick-stop device. During the machining of MMCs, elemental and arc chips formations were observed. Increasing the hardness due to high volume fraction of Al 4 C 3 in the matrix resulted in a decrease in the formation of built-up edge but increased the surface quality at high cutting speeds. It was concluded that the effect of Al 4 C 3 on the crack formation in shear plane, shortened the chip contact length and the chip segment thickness.

The effects of heat treatment on the machinability of mild steels

Abstract In this study, the effects of microstructure and mechanical properties on the machinability of hot rolled SAE 1050 steel that was annealed and normalised before machining, have been investigated. The machinability has been characterised by measuring the tool life, chip root morphology, cutting forces, surface finish, and tool/chip interface temperature. Here, the optimum machinability, especially from the stand point of tool life, has been determined for hot rolled steel which had minimum impact energy and minimum ductility. By annealing this material, a coarse pearlitic microstructure and a microstructure having 10% spherical cementite was obtained with an increasing ferrite+pearlite banding. This led to an increase in ductility and impact energy, but the decrease in hardness shortened the tool life and worsened the machinability. With normalising heat treatment, on the other hand, the banding disappeared, hardness, ductility and impact energy increased; but the tool life shortened more and more. The maximum built-up edge (BUE) thickness occurred at lower cutting speeds in machining annealed specimens. The minimum surface roughness was observed on the hot rolled specimen at final cutting speeds. The heat treatment operations applied did not bring about a considerable difference in cutting forces. A significant correlation between the machinability and the hardness of specimens could not be determined.

Friction Stir Welding of 7075-T651 Aluminium Alloy

Abstract The microstructural changes, mechanical properties and residual stress distribution of 7075-T651 Al alloy joined using friction stir welding were investigated in this study. Welding was performed at 900, 1 250, and 1 600 rev/min and 20, 40, and 60 mm/min welding speeds. Mechanical tests were carried out on the welded joints in addition to microstructural examinations performed using a scanning electron microscope. Furthermore, residual stress distribution of the joints was determined by the hole drilling method. Generally, higher tensile strength was obtained at medium rotational and welding speeds. Tunnel defects were formed in the root of the weld seam. At high welding speeds, insufficient filling in the joints led to microvoids and large grain bands on the retreating side of the weld seam. The tensile strength of the welded specimens decreased at the rate of 26 – 45 % compared to the reference material. Lower residual stresses were determined in the specimens joined at a high rotational speed.

Effect of Cutting Tool Materials on Surface Roughness and Cutting Forces in Machining of Al-Si3N4 Composite Produced by Powder Metallurgy

In this study, aluminum-based composites reinforced with various amounts of α-Si3N4 were produced by powder metallurgy (P/M). The machinability properties of MMCs were determined by means of cutting forces and surface roughness. Machining tests were carried out by using PCD and K10 cutting tools. Increasing of Si3N4 volume fraction in the matrix resulted in a decrease of the surface roughness and turning forces. PCD cutting tools showed better cutting performance than K10 tools. Surface roughness and turning forces were decreased significantly by PCD tool.

Mechanical and fracture behavior of B4C reinforced Al composites produced by hot pressing

Abstract In this study, the effects of particle addition on the microstructure, mechanical properties and fracture behaviors of Al/B4C particle reinforced composite produced by hot pressing method were investigated. After the production of 5, 10 and 15 wt.-% of B4C reinforced composites, T6 heat treatment was applied. It was specified that a strong interface bond occurred between the matrix and particles, and during the fracturing of composites, this effect increased the particle fracture. It was observed that particles were fractured parallel to the fracture surface and to each other fracture surface of MMCp. In general, cavity of particle separated from the matrix was not seen. In the production of MMCp, it was also observed that hot pressing provided a density higher than 99 %. After the heat treatment the maximum hardness value of 173 HB was reached with 15 wt.-% B4C reinforced sample. The transverse rupture strength (TRS) decreased with the increase of reinforcement ratio. The highest TRS was 510 MPa with the 5 wt.-% reinforced material, whereas the lowest value was obtained to be 387 MPa with the 15 wt.-% B4C reinforced material.

Effect of tool material on microstructure and mechanical properties in friction stir welding

Abstract Although the number of experimental studies investigating the effect of friction stir welding (FSW) parameters on joining properties have increased recently, there are not sufficient numbers of studies on the effect of the stirring tool material in friction stir welding. This study investigated the effect of stirring tool materials on microstructure, mechanical properties and residual stress of joints. Samples of 7075-T651 Al alloys were joined by FSW using uncoated and TiN-coated X210Cr12 alloy steel stirring tools. The welding processes were performed at rotational speeds of 900, 1250 and 1600 rpm and at a welding speed of 60 mm × min−1. Mechanical and metallographic tests were applied to the welded joints and residual stress analysis was performed using the hole drilling method. The best mechanical properties were determined in the welded samples joined by the uncoated tool at a rotational speed of 900 rpm. It was also determined that the TiN-coated tool negatively affected the mechanical and metallurgical properties of the weldements. Moreover, the highest longitudinal residual stresses were specified in the joining performed by the uncoated tool.

Effect of the Weld Joint Configuration on Stressed Components, Residual Stresses and Mechanical Properties

Abstract The effect of the weld joint configuration on components has been studied, which are under service loads, under repair or construction and the residual stresses as well as the mechanical properties of the joint have been determined. For this purpose, a horizontal positioned tensile testing device and a semi-automatic MIG welding machine have been used and then the weld joints of the plates were subjected to different elastic stresses. When the temperature of the joined elements decreased to room temperature, applied elastic stresses were released. By this means, the effects of the existing tensile stresses in the joined parts and the tensile stresses created by the welding processes were investigated. The tensile stresses occurring in the joined elements were determined by using the photo-elasticity analysis method and the hole-drilling method. Also, tensile-shear tests were applied in order to determine the effect of permanent tensile loads on the mechanical properties of the joint. Experimental results showed that the application of corner welded lap joints for components under tensile loading significantly decrease the shear strength and yielding capacities of the joint.

Machinability of Elongated Coarse Grain Fe-Based Superalloys

□ In conventional metal cutting process, materials are assumed to be homogeneous and isotropic structure. However, some materials with a single crystal or coarse elongated polycrystalline demonstrate strong anisotropic behavior in physical and mechanical properties in machining of some superalloy materials. The anisotropic structure always leads to variation at machinability properties of the material. In this study, machinability properties of ferritic superalloy PM2000, which had elongated a few coarse grains, were investigated. These properties were determined by investigation of chip formation, cutting forces and surface roughness. Machinability was assessed by single-point turning on a CNC lathe and turning forces were measured by using a Kistler Lathe Dynamometer. The chip formation mechanisms in machining of PM2000 at various cutting speeds were determined by using a quick-stop device (QSD). Chip roots and machined surfaces were analyzed by means of scanning electron microscopy (SEM). The results indicated that the machinability properties of the PM2000 were changed by orientated coarse grain structure. Three types chip formation mechanism were determined at the same cutting conditions. Also, surface roughness on the machined each grain changed with changing the grain to be cut. Surface roughness and force fluctuations decreased with increasing the cutting speed; however, tool wearing increased.

Effect of Foaming Agent on the Structure and Morphology of Al and Alumix 231 Foams Produced by Powder Metallurgy

In this study various amounts of foaming agent (TiH2 % 0,5-1-1,5-2 ) were added to Al and Alumix 231 powders (Al-Cu %2,5-Mg %0,5–Si %14) and mixed for 30 minutes in a three dimensional turbula. Mixed powders were compacted and then foamed freely at 690°C. Effect of foaming agent on the structure, shape and distribution of pores together with linear expansion, density of the foam and wall thickness of the cell of both materials were investigated. In all conditions foam produced from Alumix 231 powders had more homogenous distribution of the pore compare to the sample produced from pure Al powders.