Junaidi Syarif

An Overview of Semisolid Processing of Aluminium Alloys

Semisolid metal processing (SSM) or thixoforming is a new technology that offers several advantages over liquid processing and solid processing. This process utilizes semisolid behavior as well as reduces macrosegregation, porosity, and forming forces during shaping process. A lot of research work has been carried out by various researchers in order to exploit the potential of this process to produce different products especially for automotive industry. This paper will summarise the rheological behavior of aluminium alloys in semisolid slurries, thixoformability of modified aluminium alloys, the effect of feedstock production method on mechanical properties, and the importance of developing low-cost raw materials for semisolid processing.

Stability of the beta phase in Ti-Mo-Cr alloy fabricated by powder metallurgy

A new b Ti alloy was designed and fabricated by powder metallurgy process using pure metallic powders. The addition of Mo and Cr increased the stability of the b phase. By contrast, O promoted a phase formation upon cooling. The addition of 18%Mo and 10%Cr stabilized the b phase into ambient temperature. O increased the critical cooling rate of formation of a phase due to the prediction of the continuous cooling transformation diagram calculated by the Java-based Material Properties software. Sintering and solution treatment also enhanced the alloying behavior of pure powders to their designated chemical compositions. Hardness of the alloy decreased with increasing Mo and Cr content, which led to the decrease of a phase. The Ti-18%Mo-10%Cr alloy exhibited better corrosion resistance than a commercial Ti-6%Al-4%V alloy, which is used as current biomaterial.

Microstructural evolution during DPRM process of semisolid ledeburitic D2 tool steel

Semisolid metal processing is a relatively new technology that offers several advantages over liquid processing and solid processing because of the unique behaviour and characteristic microstructure of metals in this state. With the aim of finding a minimum process chain for the manufacture of high-quality production at minimal cost for forming, the microstructural evolution of the ledeburitic AISI D2 tool steel in the semisolid state was studied experimentally. The potential of the direct partial remelting (DPRM) process for the production of AISI D2 with a uniform globular microstructure was revealed. The liquid fraction was determined using differential scanning calorimetry. The microstructures of the samples were investigated using an optical microscope and a scanning electron microscope equipped with an energy dispersive spectroscopy analyser, while X-ray phase analysis was performed to identify the phase evolution and the type of carbides. Mechanical characterisation was completed by hardness measurements. The typical microstructure after DPRM consists of metastable austenite which was located particularly in the globular grains (average grain size about 50 μm), while the remaining interspaces were filled by precipitated eutectic carbides on the grain boundaries and lamellar network.

Fatigue and Mechanical Properties of Aluminium-Copper Bi-Metal Tubes

Metallurgical bonded aluminium-copper bi-metal tube has a future prospect as an alternative material to copper in the heat, ventilation and air-conditioning (HVAC) industries. The application of aluminum-copper bi-metallic material is seems practical in maintaining the quality of existing products. However, the mechanical strength and fatigue properties of the bi-metal tubes are unknown. In this study, metallurgical, mechanical and fatigue properties of the copper phosphorous alloy and aluminium-copper bi-metal tubes were characterized through metallographic analysis, tensile, bending and fatigue tests. The results show that there observed a weak and brittle Al-Cu intermetallic compound at the interlayer between Al and Cu. Tensile fracture surface observation revealed that separation of Cu from Al occurred at the interlayer. The bending properties of the tubes were influenced by the amount of volume fraction of Cu in the materials. Three point bending fatigue test results showed that a critical buckling stress is presents for tubes with diameter less than 12.7mm. The aluminium-copper bi-metal tubes show degradation of fatigue strength almost 55% as compared to that of Cu alloy tube.

Evolution of Globular Microstructures during Direct Partial Re-Melting Experiment of AISI D2 Tool Steel

Steel is a mostly challenging metal to semisolid process because of the high temperatures implicated and the prospective for surface oxidation. Slurry processing experiment was performed with AISI D2 cold work tool steel to identify the evolution of globular microstructures via Direct Partial Re-Melting Method (DPRM). Samples were heated in an argon atmosphere up to 1330°C which corresponded to about 38% of liquid fraction and held for 5 minutes. The typical microstructure after DPRM consists of globular grains (average grain size about 50μm) while the remaining interspaces were filled by precipitated eutectic carbides on the grain boundaries and lamellar network. Based on the requirements of thixoformability, the current work confirms the suitability of the AISI D2 cold work tool steel as a candidate material for semi-solid forming.

Semi-Solid Joining of D2 Cold-Work Tool Steel

Cold-work tool steel is considered to be a non-weldable metal due to its high percentage content of carbon and alloying elements. To address this problem the application of a new process of semisolid joining using a direct partial remelting method was developedto achieve a spherical join structure between two parts of AISI D2 cold-work tool steel. Since the surface oxidation of this metalis very high, the control of the atmosphere during joining had to be considered. Samples were heated in an argon atmosphere at two different temperatures of 1250°C and 1275°C for 10 minutes. Metallographic analyses along the joint interface showed that an increase in temperature promoted the final joining properties and also that at a liquid fraction of 15% joining was not fully practicable. However, a20% liquid fraction can produce a very good joint and microstructure as compared to the other experimental liquid fraction. Metallographic analyses along the joint interface showed a smooth transition from one to the other and neither oxides nor microcracking was observed. The current work confirmed that avoidance of a dendritic microstructure in the semisolid joined zone and high bonding quality components can be achieved without the need for force or complex equipment when compared to conventional welding processes.

HA/Ti6Al4V Powder with Palm Stearin Binder System - Feedstock Characterization

Metal Injection Molding (MIM) is widely known as net shape process to mass production for complex shape. In this study polyethylene and palm stearin was used as binder system for composite HA and Ti6Al4V. Ti6Al4V has spherical shape with particle size 25 μm and Hydroxyapatite has particle size 5 μm. Brabender® was used to mix HA and Ti6Al4V powder and binder for making feedstock, rheological properties of feedstock was examined by capillary rheometer. Effects of temperature, viscosity, shear rate and activation energy were discussed in this paper. Binder was removed by thermal debinding. Rheological test showed feedstock of composite HA and Ti6Al4V shows pseudoplastic behavior. Sintering was conducted on 1200°C by argon with holding time 2 hour.

Comparison of Dry and Cryogenic Machining on Chip Formation and Coefficient of Friction in Turning AISI 4340 Alloy Steel

Application of cutting fluid that provides both coolant and lubrication properties in manufacturing operations such as turning, milling, grinding and other processes has been proven to improve the machining output in many aspects. In cryogenic machining, liquid nitrogen (LN2) is used as cutting fluid to reduce the temperature generated at the cutting zone. However, there is still an issue being raised on whether LN2 also functions as a good lubricant as it does as an excellent coolant. Therefore, an intensive study on the chip formation during dry and cryogenic turning of AISI 4340 alloy steel has been conducted to examine the effect of LN2 cutting fluid on the reduction of friction between the chip and the tool. Results from calculation of coefficient of friction indicate that application of LN2 during turning is able to help the friction reduction up to 73%. Smaller value of coefficient of friction indicates that the shear angle is larger which results in smaller shear plane area that provides benefits of lower cutting force needed to shear off the chips and lower cutting temperature being generated during the machining process.

Study on Microstructure and Tensile Properties of New Cu-Al Bi-Metal Tubes Versus Pure Copper Tubes

In recent years, heating, ventilation and air condition (HVAC) industries have attempted to find alternative materials such as aluminum for replacing copper metal because of a light weight metal with relatively lower market price compared to copper. This study characterizes microstructure and tensile properties of new Cu-Al bi-metal tubes (aluminum cladded copper (ACC) and copper cladded aluminum (CCA)) versus copper phosphorous alloy tube in order to estimate the possibility of implementing the composite tubes in heating, ventilation, and air conditioning industries. The result shows that Cu phosphorus alloy tubes has the highest tensile properties followed by CCA and ACC bi-metal tubes and different tube size does not affect the tensile properties of tube of the same type.

Effect of Pouring Temperature and Cooling Slope Length on Microstructure and Mechanical Properties of Rheocast A319 Aluminium Alloy

Aluminium alloys are among the most prominent and well known materials used in automotive industries. Nowadays, many vehicles used aluminium engine blocks instead of cast iron to improve fuel efficiency. Among cast aluminium alloys, A319 grade alloys are normally used in automotive industries due to a combination of good fluidity and mechanical strength. In this study, A319 cooling slope rheocasting billets were produced in order to obtain near spherical morphology of primary aluminium phase. The change in the α-Al morphology upon the cooling slope casting was remarkable and the dendritic microstructure was almost replaced by α-Al globules and rosettes. The rheocasting billets were prepared for tensile testing at room temperature. It is found that, the yield strength and elongation of cooling slope rheocasting billets is higher than those from as-cast A319 alloy.