Role of sr on microstructure, mechanical properties, wear and corrosion behaviour of an al-mg2si-cu in-situ composite

The influence of Sr additions on the microstructure of primary and eutectic Mg2Si phases, wear and corrosion behaviour of Al–Mg2Si–Cu in-situ composite was investigated. The results showed that addition of 0.01 wt% Sr modified the primary Mg2Si morphology but exceeding this level of Sr induced a loss of modification as the primary phase morphology coarsened again. The Al–Mg2Si eutectic phase, on the other hand, still exhibited a refined structure even with higher levels of Sr additions. Thermal analysis results revealed that both modification of the primary Mg2Si and refinement of the eutectic Mg2Si are most likely related to nucleation and growth stages respectively. The results of 0.01 wt% Sr addition showed that the mean size and mean aspect ratio decreased by about 30% and 6% respectively, but the mean density increased by 185% respectively. The highest UTS, El%, impact toughness and hardness were measured at 101.57 MPa, 1.1%, 1.31 J and 81 VHN respectively. Fractography of tensile and impact specimens from the Sr-treated composite revealed that Mg2Si particles suffered cracking with few decohesion indicating higher ductility. The results of wear testing also showed that composites treated with Sr have higher wear resistance compared with those of without Sr. The highest resistance to wear was observed in the composite containing 0.01 wt %Sr which is likely the result of good dispersion of fine Mg2Si particles in the Al matrix. This fine morphology and uniform distribution of Mg2Si particles also contributed to better corrosion resistance by reducing the propagation of corrosion pits

Adhesion strength of HFCVD diamond coating on WC substrate seeded with diamond and different ratios of SiC powders

The effect of seeding using different mixtures of diamond and silicon carbide (SiC) powders on the adhesion strength of hot-filament chemical vapor deposition (HFCVD) diamond coating on WC-6% Co substrates was studied. Diamond powders with the average grain size of 0.5 µm mixed with various concentrations of SiC powder of 175µm average grain size were employed. Diamond layers were deposited using a production unit of HFCVD technique. The diamond film morphology and the diamond quality were examined using field emission scanning electron microscope (FESEM), X-ray diffraction (XRD) and Raman spectrometer respectively. It was found that the diamond morphologies produced and the qualities were almost the same for all the seeding mixtures of pretreatment. With the blasting technique employed to determine the adhesion strength it was found that the highest diamond film adhesion strength was achieved from the seeding of a mixture of diamond with 5g/l SiC powder

Effect of heat treatment on the diffusion coefficient of hydrogen absorption in gamma-titanium aluminide

Intermetallic alloys based on gamma-titanium aluminide are now regarded as promising candidate materials for high temperature applications such as for aerospace, marine and automotive engine components, due to their high specific strength and modulus. Their oxidation resistance is good, especially at intermediate and high temperature; oxidation resistance can be obtained up to 800 °C. One critical area of application is in combustion engine in aerospace vehicles such as hypersonic airplanes and high-speed civil transport airplanes. This entails the use of hydrogen as a fuel component and it has been widely reported by researchers that these materials exhibit environmental embrittlement in the presence of hydrogen, hence the diffusivity of hydrogen and the effect of hydrogen to the mechanical properties of ?-titanium aluminide is significant and technologically important. A fair amount of research has been carried out to investigate the influence of hydrogen in ?-titanium aluminide. Some researchers reported that a2 and lamellar phases had major influence on the susceptibility of hydrogen to alloys, while hydrogen is too low to penetrate the ?-phases. This research focused on the effect of different microstructures obtained from various heat treatments to the diffusion coefficient and mechanical property after hydrogen absorption. Modification of ?-titanium aluminide can be achieved by heating as-cast binary samples; Ti–45% Al up to 1200 °C (above the Te line) and cooled in three different ways: quenched, air-cooled and furnace-cooled. All samples were then subjected to corrosion attack under cathodically charged with galvanostatic mode for 6 h. The potential variation with time was monitored from these data the values of the diffusion coefficient of hydrogen to -titanium aluminide. D was calculated based on Fick's second law. This result was compared with that obtained from micro-Vickers hardness profiling, which was measured at cross-section area per depth from the top surface corroded. Hydrides formed at the surface were analysed by using image analyser, scanning electron microscopes (SEM) and X-ray diffraction (XRD) equipment. The results showed that different microstructures have an effect on the diffusion coefficient and mechanical property after hydrogen absorption

Influence of Difference Solders Volume on Intermetallic Growth of Sn-4.0Ag-0.5Cu/ENEPIG

In recent years, portable electronic packaging products such as smart phones, tablets, notebooks and other gadgets have been developed with reduced size of component packaging, light weight, high speed and with enhanced performance. Thus, flip chip technology with smaller solder sphere sizes that would produce fine solder joint interconnections have become essential in order to fulfill these miniaturization requirements. This study investigates the interfacial reactions and intermetallics formation during reflow soldering and isothermal aging between Sn-4.0Ag-0.5Cu (SAC405) and electroless nickel/immersion palladium/immersion gold (EN(P)EPIG). Solder diameters of 300 μm and 700 μm were used to compare the effect of solder volume on the solder joint microstructure. The solid state isothermal aging was performed at 125°C starting from 250 hours until 2000 hours. The results revealed that only (Cu,Ni)6Sn5 IMC was found at the interface during reflow soldering while both (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 IMC have been observed after aging process. Smaller solder sizes produced thinner IMC than larger solder joints investigated after reflow soldering, whereas the larger solders produced thinner IMC than the smaller solders after isothermal aging. Aging duration of solder joints has been found to be increase the IMC’s thickness and changed the IMC morphologies to spherical-shaped, compacted and larger grain size

Effect of pouring temperature and melt treatment on microstructure of lost foam casting of AL-Si LM6 alloy

This paper presents the experimental investigation conducted on Al-Si cast alloy (LM6) cast using lost foam process. The main objective of the research is to investigate the effect of pouring temperature, section thickness and melt treatment on the microstructure of the lost foam casting of Al-Si alloy. Step pattern with five different sections was prepared from 20 kg/m3 density foam and poured at five different temperatures; 700, 720, 740, 760, and 780°C with and without the addition of AlTiB as grain refiner. Analysis on microstructure, eutectic silicon spacing and porosity percentage were conducted to determine the effect of both parameters. The results show that pouring temperature has significant influence on the quality as well as microstructure of the lost foam casting of LM6 Al-Si alloy. Lower pouring temperature was found to produce finer microstructure casting. However, the addition of AlTiB as grain refiner did not affect the produced castings significantly whether in terms casting quality or microstructure

Effect of solder bump size on interfacial reactions during soldering between Pb-free solder and Cu and Ni/Pd/Au surface finishes

Flip chip technology provides the ultimate in high I/ O-density and count with superior electrical performance for interconnecting electronic components. Therefore, the study of the intermetallic compounds was conducted to investigate the effect of solder bumps sizes on several surface finishes which are copper and Electroless Nickel/ Electroless Palladium/ Immersion Gold (ENEPIG) which is widely used in electronics packaging as surface finish for flip-chip application nowadays. In this research, field emission scanning electron microscopy (FESEM) analysis was conducted to analyze the morphology and composition of intermetallic compounds (IMCs) formed at the interface between the solder and UBM. The IMCs between the SAC lead-free solder with Cu surface finish after reflow were mainly (Cu, Ni)6Sn5 and Cu6Sn5. While the main IMCs formed between lead-free solder on ENEPIG surface finish are (Ni, Cu)3Sn4 and Ni3Sn4. The results from FESEM with energy dispersive x-ray (EDX) have revealed that isothermal aging at 150 degree Celsius has caused the thickening and coarsening of IMCs as well as changing them into more spherical shape. The thickness of the intermetallic compounds in both finishes investigated was found to be higher in solders with smaller bump size. From the experimental results, it also appears that the growth rate of IMCs is higher when soldering on copper compared to ENEPIG finish. Besides that, the results also showed that the thickness of intermetallic compounds was found to be proportional to isothermal aging duration

Microstructure characterization, mechanical, and tribological properties of slow-cooled Sb-treated Al-20Mg2Si-Cu in situ composites

Role of Sb addition on structural characteristics, mechanical properties, and wear behavior of Al-20Mg2Si-Cu in situ composite under slow cooling condition was thoroughly investigated in this study using stereomicroscopy, optical and scanning electron microscopy, thermal analysis, tensile, impact, hardness tests, and wear tester. Results show that addition of 0.8 wt.% Sb was found to produce a change in the morphology of primary Mg2Si from dendrite to fine polygonal shape. At this Sb addition, the primary Mg2Si phase also exhibited a reduction in size from 179.4 to 128.6 μm, an increase in density of Mg2Si per area from 12.5 to 32.2 particle/mm2, and a decrease in the aspect ratio from 1.24 to 1.11. Increasing the amount of Sb added up to 1 wt.% also resulted in a decrease in both nucleation and growth temperatures of the eutectic Mg2Si by 2.6 and 1.7 °C respectively, which is most likely due to change of eutectic Mg2Si morphology from flake to fibrous structure. Thermal analysis technique showed that distribution of Mg2Si particles influences the heat conductivity during the solidification process of Al-Mg2Si composite. The results also showed that improvements in mechanical properties of composite were obtained with increasing Sb content due to modification of both primary and eutectic Mg2Si and due to intermetallic compound transformation from β-Al5FeSi to α-Al15(Fe,Mn)3Si2. Examination of fracture surfaces from tensile and impact samples showed that the base composite failed in a brittle manner with decohered or debonded Mg2Si particles, whereas the 0.8 wt.% Sb-treated composite showed more cracked Mg2Si and ductile fracture in the matrix. Wear properties improved significantly with addition of Sb due to modification and better dispersion of fine Mg2Si particles in matrix

Study on interfacial reaction between lead-free solders and alternative surface finishes

This study investigates the interfacial reactions occurring during reflow soldering between Sn-Ag-Cu lead-free solder and two surface finishes: electroless nickel/ immersion gold (ENIG) and immersion silver (IAg). The study focuses on interfacial reactions evolution and growth kinetics of intermetallic compounds (IMC) formed during soldering and isothermal ageing at 150 degree Celsius for up to 2000 hours. Optical and scanning electron microscopy were used to measure IMC thickness and examine the morphology of IMC respectively, whereas the IMC phases were identified by energy dispersive X-ray analysis (EDX). The results showed that the IMC formed on ENIG finish is thinner compared to that formed on IAg finish. For IAg surface finish, Cu6Sn5 IMCs with scallop morphology are formed at the solder/ surface finish interface after reflow while a second IMC, Cu3Sn was formed between the copper and Cu6Sn5 IMC after the isothermal ageing treatment. For ENIG surface finish both (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 are formed after soldering. Isothermal aging of the solder joints formed on ENIG finish was found to have a significant effect on the morphology of the intermetallics by transforming to more spherical and denser morphology in addition to increase i their thickness with increased ageing time

Effect of applying air pressure on gas porosity in lost foam casting of al-si alloy

The paper presents the result of investigation on aluminum-silicon (LM6) alloy cast using pressurized lost foam casting process. The study investigated the effect of pressure and sand size on porosity of the casting produced. Air pressure of 1, 2, 3 and 4 bars was applied on the solidifying alloy poured in mould of sand sizes 16-30, 40-60, 60-100 (AFS). The porosities of casting were measured using optical microscope which was equipped with image analyzer. For porosity of castings, all surfaces of solidified castings were captured by digital camera for better observation. The results show that applying pressure during solidification of the LM6 alloy has significant influence on casting porosity of the alloy. By increasing the applied pressure, the porosity percentage based on gas porosity decreased when pressure was applied. Consequently, the removal rate of gas porosity improved by increasing the sand size to finer size 60-100 (AFS), so there is less gas porosity in samples. Besides, rising air pressure lead to fulfilling of molten which improves the casting porosity