Zainuddin Sajuri

Effect of strain rates on tensile and work hardening properties for Al-Zn magnesium alloys

The effect of strain rate on the mechanical behavior of Al-Zn magnesium alloys was examined in room temperature from low to high strain rates by using a Universal Testing Machine. Quasi static tensile test was performed in four different strain rates to obtained their effect on tensile properties and work hardening rate using a round shape tensile sample. Two types of Al-Zn magnesium alloys were used in this research study i.e. AZ31 and AZ61 magnesium alloys. The yield stress and tensile strength of AZ31 were found to be strain rate dependent but not for AZ61. The elongation of AZ31 were approximately about 15% for all strain rate levels but for AZ61 the elongations were slightly decreased with increasing strain rates. For all strain rate levels, the work hardening rate of AZ61 were found higher compared to that of AZ31. The change in fracture mode as observed from the fracture surface implies that the fracture mechanisms in AZ31 change as the strain rate increases.

High Cycle Fatigue Behavior of Magnesium Alloys under Corrosive Environment

The high cycle fatigue characteristics of magnesium alloys under low humidity, high humidity (80% RH) and sprayed 5%NaCl solution environments have been introduced. Fatigue limit of bulk magnesium alloy was significantly reduced even under high humidity condition, while other structural materials such as steel and aluminum alloy showed no influence of humidity on fatigue limit. The reduction of fatigue limit under 5% NaCl environments was much larger than that under high humidity environment. The remarkable reduction of fatigue limit under corrosive environments was attributed to the formation of corrosion pit, which was induced by simultaneous action of mechanical loading and corrosive environment. To improve the reduced fatigue strength under corrosive environment, coating used to apply on the surface. Non-chromium chemical conversion coating showed superior effect on the improvement of fatigue strength under corrosive environment compared to anodized coating. Fatigue strengths of the coated and painted AZ61 alloy under high humidity and 5%NaCl environments showed almost the same fatigue strength as bulk material under low humidity.

Enhancing material performance through laser surface texturing: a review

Materials with well-defined surface structures are prepared using protective coatings through surface texturing, which is a novel method for modifying surface characteristics, particularly tribological and wettability, to improve the properties of material parts. The formation of a specific patterned surface can be achieved through abrasive blasting, reactive-ion etching, lithography and mechanical machining. This review focuses on laser technology because it generates the most controllable and precise geometries. This technique is environmentally friendly because it does not utilise any chemical reagent, nor does it produce significant waste.

Effect of strain rate on tensile and work hardening properties for Al-Zn magnesium alloys

The effect of strain rate on the mechanical behaviour of Al-Zn magnesium alloys was examined at room temperature under tensile loading with wide range of strain rate. Quasi static tensile test was performed in four different strain rates to obtain their effect on tensile properties, work hardening rate, strain hardening exponent and strength coefficient using a round shape tensile sample. Two types of Al-Zn magnesium alloys were used in this research study, i.e., AZ31 and AZ61 magnesium alloys. The yield stress and tensile strength of AZ31 were found to be strain rate dependent but not for AZ61. The elongations of AZ31 were approximately about 15% for all strain rate levels but for AZ61 the elongations were slightly decreased with increasing strain rate. For all strain rate levels, the work hardening rate of AZ61 was found to be higher compared to that of AZ31. The strain hardening exponent was decreased with increasing strain rate. In contrast, the strength coefficient was increased with increasing strain rate for both alloys. The change in fracture mode as observed from the fracture surface implies that the fracture mechanisms in AZ31 change as the strain rate increases.

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.

BALLISTIC LIMIT OF HIGH-STRENGTH STEEL AND AL7075-T6 MULTI-LAYERED PLATES UNDER 7.62-MM ARMOUR PIERCING PROJECTILE IMPACT

THIS PAPER PRESENTS THE COMPUTATIONAL-BASED BALLISTIC LIMIT OF LAMINATED METAL PANELS COMPRISED OF HIGH STRENGTH STEEL AND ALUMINIUM ALLOY AL7075-T6 PLATE AT DIFFERENT THICKNESS COMBINATIONS TO NECESSITATE THE WEIGHT REDUCTION OF EXISTING ARMOUR STEEL PLATE. THE NUMERICAL MODELS OF MONOLITHIC CONFIGURATION, DOUBLE-LAYERED CONFIGURATION AND TRIPLE-LAYERED CONFIGURATION WERE DEVELOPED USING A COMMERCIAL EXPLICIT FINITE ELEMENT CODE AND WERE IMPACTED BY 7.62 MM ARMOUR PIERCING PROJECTILE AT VELOCITY RANGE OF 900 TO 950 M/S. THE BALLISTIC PERFORMANCE OF EACH CONFIGURATION PLATE IN TERMS OF BALLISTIC LIMIT VELOCITY, PENETRATION PROCESS AND PERMANENT DEFORMATION WAS QUANTIFIED AND CONSIDERED. IT WAS FOUND THAT THE MONOLITHIC PANEL OF HIGH-STRENGTH STEEL HAS THE BEST BALLISTIC PERFORMANCE AMONG ALL PANELS, YET IT HAS NOT CAUSED ANY WEIGHT REDUCTION IN EXISTING ARMOUR PLATE. AS THE WEIGHT REDUCTION WAS INCREASED FROM 20-30%, THE DOUBLE-LAYERED CONFIGURATION PANELS BECAME LESS RESISTANCE TO BALLISTIC IMPACT WHERE ONLY AT 20% AND 23.2% OF WEIGHT REDUCTION PANEL COULD STOP THE 950M/S PROJECTILE. THE TRIPLE-LAYERED CONFIGURATION PANELS WITH SIMILAR AREAL DENSITY PERFORMED MUCH BETTER WHERE ALL PANELS SUBJECTED TO 20-30% WEIGHT REDUCTIONS SUCCESSFULLY STOPPED THE 950 M/S PROJECTILE. THUS, TRIPLE-LAYERED CONFIGURATIONS ARE INTERESTING OPTION IN DESIGNING A PROTECTIVE STRUCTURE WITHOUT SACRIFICING THE PERFORMANCE IN ACHIEVING WEIGHT REDUCTION.

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.

Microstructural morphology of rheocast A319 aluminium alloy

This article examines the evolution of the microstructure of A319 aluminium alloy as it flows along a cooling slope plate and discusses the type and influence of the intermetallic compounds thus formed. Numerous past research studies have analysed the microstructural transformation of alloys in a mould, but few researchers have investigated this phenomenon on the cooling slope plate. A change in the microstructure of the alloy from dendritic to non-dendritic is clearly obtained as the alloy moves from the impact zone to bottom zone on the cooling slope plate. It is important to clarify the mechanism of microstructural evolution through nucleation and fragmentation of the primary phase arm for fundamental understanding of research. Analysis by optical microscope and scanning electron microscope reveals the evolution of the microstructure and intermetallic compounds of A319 as it progresses along the cooling slope plate. The Vickers test was used to determine the hardness of the alloy thus produced. The results show the influence of the mould in obtaining a spheroidal microstructure; the microstructure in the bottom zone of the cooling slope plate is nearly spheroidal rather than fully spheroidal. The hardness of the alloy is enhanced when the microstructure is spheroidal and when the Mg2Si compound is present in the alloy.

Evaluating the Effect of Mixing Process on Nano-Clay Modified Binders Using the Pull-Off Test Method

Bonding strength of bitumen is one of the most important properties in need of independent evaluation. Conducting a pull-off test to determine the bonding strength of bitumen can be done using the Universal Test Machine (UTM). In this work, the UTM was used to investigate the effect of adding an additive to with a 60/70 penetration grade bitumen; the additive used was nano-clay at a percentage of 2% and 4%. A designed mold was fabricated and used with granite and stainless steel substrates. The investigation covered the influence of variation in the mixing process (mixing duration and power of rotation during mix) on the bonding strength of the samples. X-ray diffraction (XRD) was used to discover the nano-clay exfoliation within the binder structure. Also, empirical tests - penetration and softening point tests - were conducted. The results varied according to variation in percentage of additive, substrates used and the mixing process. The bonding strength and softening point results were able to identify the effect of the additive, and were able to detect changes caused by the adding condition; both were very well correlated, unlike the penetration test result which had a weaker correlation with bonding strength.

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.