Thawatchai Plookphol

Microstructure Evolution during Solution Heat Treatment of Semisolid Cast 2024 Aluminum Alloy

The aim of this study is to determine the appropriate solution treatment temperature and time of semi solid 2024 Al alloy. Solution heat treatment at 450°C and 480 °C for various times, from 4 hours to 16 hrs, were applied followed by artificial aging at 220 °C for 1 hr. Microstructure of the semi solid cast 2024 aluminum alloy mainly showed globular grain structure which consisted of matrix-α (Al) and grain boundary (GB) - eutectic phases (α+Al2CuMg/Al2Cu). Eutectic GB phases was found to completely dissolved after solution heat treatment at 480°C for 14 hrs while sample solution treated at 450°C for the same time showed the existence of remaining GB phases. Prolonging heat treatment after 14 hrs at both temperatures resulted in the formation of coarse black particles at the grain boundaries which were identified as Mg2Si phases. Therefore the suitable solution treatment of the alloy in this study was at 480°C for 14 hrs.

Load Relaxation of Olivine Single Crystals

Single crystals of ferromagnesian olivine (San Carlos, AZ, peridot; ~Fo88-90) have been deformed in both uniaxial creep and load relaxation under conditions of ambient pressure, T = 1500 °C and pO2= 10–10 atm; creep stresses were in the range 40 ≤ σ1 (MPa) ≤ 220. The crystals were oriented such that the applied stress was parallel to [011]c, which promotes single slip on the slowest slip system in olivine, (010)[001]. The creep rates at steady state match well the results of earlier investigators, as does the stress sensitivity (a power-law exponent of n = 3.6). Dislocation microstructures, including spatial distribution of low-angle (subgrain) boundaries additionally confirm previous investigations. Inverted primary creep (an accelerating strain rate with an increase in stress) was observed. Load-relaxation, however, produced a singular response—a single hardness curve—regardless of the magnitude of creep stress or total accumulated strain preceding relaxation. The log-stress v. log-strain rate data from load-relaxation and creep experiments overlap to within experimental error. The load-relaxation behavior is distinctly different than that described for other crystalline solids, where the flow stress is affected strongly by work hardening such that a family of distinct hardness curves is generated, which are related by a scaling function. The response of olivine for the conditions studied, we argue, indicates flow that is rate-limited by dislocation glide, reflecting specifically a high intrinsic lattice resistance (Peierls stress).

Effects of Solid Fractions in a Slurry Die Casting Process on Defects of 7075 Aluminum Alloy

The effects of Gas Induced Semi-Solid (GISS) in the slurry die casting process on defects of 7075 aluminum alloy were studied, different initial solid fractions with 10, 15, and 20 sec of rheocasting time were investigated. The results showed that the percentage of porosity in semi-solid die casting was smaller than in the liquid die casting. In terms of the initial solid fraction in 7075 aluminum alloy, it was found that the defects were found when the initial solid fraction was high. In addition.

Design and Development of a Centrifugal Atomizer for Producing Zinc Metal Powder

In the present work a preliminary design of a centrifugal atomizer for producing zinc metal powder was studied. In the design process, the consumed power and the atomizing disc size were first estimated. The trajectory of flying melt droplet from the edge of atomizer disc and the temperature profile were predicted using a concept of heat transfer in an external flow for calculating the size of atomizer chamber. A simple laboratory-scale atomizer was built. The performance of the atomizer was studied by using pure zinc metal as a model material. The effects of rotating disc speed on median particle size, particle size distribution and standard deviation, production yield, and morphology of the atomized zinc powder were investigated. The atomization was carried out using graphite flat disc, melt pouring temperature, preheating disc temperature and melt feed rate of 40 mm, 550 °C, 300 °C and 50 kg/h, respectively. The atomizer disc speeds were varied from 10,000 to 30,000 rpm. It was evidenced from the experimental results that the median particle size and standard deviation of zinc metal powder decreased with increasing disc speed. The production yield tended to increase with increasing rotating speed. SEM images revealed that most zinc metal particles were irregular, elongated flakes. The produced zinc power in this study may be suitable for use as a friction material for manufacturing brake pad in the automotive part industry.

Influence of Solution Heat Treatment on Microstructures of Semisolid Cast 7075 Aluminium Alloy

Influence of temperature and time of solution heat treatment on the microstructures of rheo-casting 7075 aluminium alloy produced by a novel technique, the Gas Induced Semi Solid (GISS) technique, had been investigated in this study. The microstructure of the as-cast specimens mainly consisted of matrix-α (Al) and grain boundary (GB)-eutectic phase (α-Al + Mg(Zn,Cu,Al)2). After solution heat treatment at 480 °C for 1 h, MgZn2 phase at the grain boundary was observed to have dissolved and coarse black particles of Mg2Si were observed to form in the matrix. In comparison, when solutionizing temperature of 450 °C was applied, it took 4 h of solution treatment time in order to dissolve the same portion of GB phase and MgZn2 phase, and coarse black particles of Mg2Si were found to form in the 8 h solution treated sample.

The Effects of Antimony Addition on the Microstructural, Mechanical, and Thermal Properties of Sn-3.0Ag-0.5Cu Solder Alloy

In this study, we investigated the effects produced by the addition of antimony (Sb) to Sn-3.0Ag-0.5Cu-based solder alloys. Our focus was the alloys’ microstructural, mechanical, and thermal properties. We evaluated the effects by means of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), differential scanning calorimetry (DSC), and a universal testing machine (UTM). The results showed that a part of the Sb was dissolved in the Sn matrix phase, and the remaining one participated in the formation of intermetallic compounds (IMCs) of Ag3(Sn,Sb) and Cu6(Sn,Sb)5. In the alloy containing the highest wt pct Sb, the added component resulted in the formation of SnSb compound and small particle pinning of Ag3(Sn,Sb) along the grain boundary of the IMCs. Our tests of the Sn-3.0Ag-0.5Cu solder alloys’ mechanical properties showed that the effects produced by the addition of Sb varied as a function of the wt pct Sb content. The ultimate tensile strength (UTS) increased from 29.21 to a maximum value of 40.44 MPa, but the pct elongation (pct EL) decreased from 48.0 to a minimum 25.43 pct. Principally, the alloys containing Sb had higher UTS and lower pct EL than Sb-free solder alloys due to the strengthening effects of solid solution and second-phase dispersion. Thermal analysis showed that the alloys containing Sb had a slightly higher melting point and that the addition amount ranging from 0.5 to 3.0 wt pct Sb did not significantly change the solidus and liquidus temperatures compared with the Sb-free solder alloys. Thus, the optimal concentration of Sb in the alloys was 3.0 wt pct because the microstructure and the ultimate tensile strength of the SAC305 solder alloys were improved.

Influence of Indium and Antimony Additions on Mechanical Properties and Microstructure of Sn-3.0Ag-0.5Cu Lead Free Solder Alloys

In this research, we investigated the influence of indium and antimony additions on the microstructure, mechanical and thermal properties of Sn-3.0Ag-0.5Cu lead free solder alloys. The results revealed that the addition of 0.5 wt.%InSb into SAC305 solder alloys resulted to a reduced melting temperature by 3.8 °C and IMCs phases formed new Ag3(Sn,In) and SnSb in the Sn-rich matrix with a decreased grain size of 28%. These phases improved the mechanical properties of solder alloys. In addition, the mechanical properties of SAC305 solder alloys increased by adding 0.5 wt.%InSb, resulting in an increase of ultimate tensile strength of 24%, but the percent elongation decreased to 45.8%. Furthermore, the Vickers microhardness slightly increased of the SAC305 solder alloys.

Effect of Cooling Rate on the Microstructure and Mechanical Properties of Sn-0.7wt.%Cu Solder Alloy

The dependence of microstructure and mechanical properties of Sn-0.7wt.%Cu solder alloys on different cooling rates were investigated. Two cooling rates were employed during solidification: 0.04 °C/s (mold-cooled system) and 1.66 °C/s (water-cooled system). The results showed that the ultimate tensile strength of Sn-0.7wt.%Cu solder alloy increased but the elongation decreased when water-cooled system was used. The microstructure of Sn-0.7wt.%Cu solder alloys solidified by both cooling systems exhibited two phases of Sn-rich and Cu6Sn5 intermetallic compounds (IMCs). However, finer grains were observed in the water-cooled specimens.

Paraffin Wax Powder Production by Ultrasonic Atomization

This work was aimed to study wax powder production from the paraffin melt by using ultrasonic atomization process. Effects of atomization operating parameters: melt temperature, melt flow rate and ultrasonic vibration amplitude on particle size distribution, median particle size, production yield and morphology of the atomized paraffin wax powder were investigated. It was evidenced from the experimental results that the particle size distribution of paraffin wax powder was narrowed and the median particle size was decreased with decreasing the melt flow rate, the vibration amplitude and increasing the melt temperature. The production yield of paraffin wax powder tended to increase with decreasing the melt flow rate, the vibration amplitude and increasing the melt temperature. The atomized paraffin wax powder was spherical shape with rough surface and some particles were formed as satellites.

Wettability of Carbon Nanotubes with Molten Sn-Ag-Cu Solder Alloy

The purpose of this work was to study the wettability of single-walled carbon nanotube (SWCNTs) and molten 96.5Sn-3.0Ag-0.5Cu (SAC305) lead-free solder alloy. The SWCNTs was coated with silver (Ag) by using an electroless plating method in order to enhance its wettability. The wetting behavior of molten SAC305 alloy on three different substrates, alumina, un-coated SWCNTs and Ag-coated SWCNTs was investigated by employing a modified sessile drop technique. The wetting angle between the molten SAC305 and the three substrates was measured at temperature range of 250-550 °C. The average wetting angles between the molten SAC305 and the alumina, the un-coated SWCNTs and the Ag-coated SWCNTs substrates were 130.7±1.3°, 128.4±4.2° and 120.1±3.5°, respectively. The wettabilty of the SWCNTs was improved by coating it with silver. The wetting angle of the Ag-coated SWCNTs was decreased approx. 9° compared to that of the un-coated. Increasing temperature has slightly affected on the wettability of SWCNTs and the molten SAC305.