bluuebunny/crossref_metadata_2025 huggingface dataset:
Annealing of Aluminum Implanted 4H-SiC: Comparison of Furnace and Lamp Annealing
Authors: Rambach Martin , Bauer Anton J. , Frey Lothar , Friedrichs Peter , Ryssel Heiner
Published: March 2009

Furnace annealing and lamp annealing of aluminum implanted layers in 4H silicon carbide (SiC) were investigated with respect to surface degradation and electrical parameters. A sheet resistance of about 20kW/ı was obtained for an aluminum implantation dose of 1.2×1015cm-2 and annealing in the furnace at 1700°C for 30min. For the same implantation dose, lamp annealing at 1770°C for 5min resulted in a three times higher sheet resistance of 60kW/ı. The surface roughness
was best for the lamp system and stayed below 1nm for Al doses lower than 1×1015cm-2.
P-Type SiC Layers Formed by VLS Induced Selective Epitaxial Growth
Authors: Lazar Mihai , Jacquier Christophe , Dubois Christiane , Raynaud Christophe , Ferro Gabriel , Planson Dominique , Brosselard Pierre , Monteil Yves , Chante Jean-Pierre
Published: March 2009

Al-Si patterns were formed on n-type 4H-SiC substrate by a photolithographic process including wet Al etching and Si/SiC reactive ion etching (RIE) process. RF 1000°C annealing under C3H8 flow was performed to obtain p+ SiC layers by a Vapour-Liquid-Solid (VLS) process. This method enables to grow layers with different width (up to 800 µm) and various shapes. Nevertheless
the remaining Al-based droplets on the largest patterns are indicators of crack defects, going through the p+ layer down to the substrate. SIMS analyses have shown an Al profile with high doping concentration near the surface, high N compensation and Si/C stoechiometry variation between the substrate and the VLS layer. The hydrogen profile follows the Al profile in the VLS layer with an overshoot at the VLS/substrate interface. I-V measurements performed directly on the
semiconductor layers have confirmed the formed p-n junction and allowed to measure a sheet resistance of 5.5 kW/ı
Effects of Dislocations on Reliability of Thermal Oxides Grown on n-Type 4H-SiC Wafer
Authors: Senzaki Junji , Kojima Kazutoshi , Kato Tomohisa , Shimozato Atsushi , Fukuda Kenji
Published: March 2009

The effects of dislocations in n-type 4H-SiC(0001) epitaxial wafers on the reliability of thermal oxides have been investigated. Charge-to-breakdown (QBD) values of thermal oxides decrease with increase in the dislocations under a gate-oxide area. Nomarski microscope observations show that dielectric breakdown of thermal oxides occurs at the position of dislocation in epitaxial layer. It is reavealed that basal plane dislocation is the most common cause of the dielectric breakdown.
Competition between Oxidation and Recrystallization in Ion Amorphized (0001) 6H-SiC
Authors: Poggi Antonella , Parisini Andrea , Solmi Sandro , Nipoti Roberta
Published: March 2009

The wet oxidation of (0001), Si-face, 6H-SiC pre-amorphised by Ar+ implantation has been investigated in the temperature range between 750 and 950 °C. Electron microscopy analysis has been performed to obtain information on the evolution of the amorphous layer during the oxidation process. When the oxidation occurs on the amorphous substrate the observed rate is given by VOx(a)=3.8x107exp(-1.6eV/kT) nm/min, by far faster than that observed on single or
polycrystalline 6H-SiC. For amorphous layer thickness of a few hundreds nanometer and processing time of a few tens of minutes this happens up to oxidation temperatures of about 910 °C, owing to the concomitant recrystallization process. At higher temperature, our oxidation data support the existence of a sudden variation of the recrystallization process that rapidly reduces the residual
amorphous region and, consequently, the oxide thickness. However, it appears that this second recrystallization stage is faster than previously estimated. Structural detail of the starting amorphous-crystalline interface and of the early-recrystallized layers are reported and discussed.
Improvement in Electrical Performance of Schottky Contacts for High-Voltage Diode
Authors: Nakamura Tomonori , Miyanagi Toshiyuki , Tsuchida Hidekazu , Kamata Isaho , Jikimoto Tamotsu , Izumi Kunikaza
Published: March 2009

We investigated the effect of high temperature annealing on the Schottky barrier height (Fb) and the ideality factor (n-factor) of a Mo contact. In a Mo contact, the Fb increased and the leakage current decreased by annealing at 600oC, while no increase in n-factor and forward excess current owing to the high temperature annealing was observed. The Schottky barrier diode with Mo contact annealed at 600oC showed a blocking-voltage (Vb) of 4.15 kV and a specific on resistance
(Ron) of 9.07 mWcm2, achieving a high Vb 2/Ron value of 1898 MW/cm2.
4H-SiC DMOSFETs for High Speed Switching Applications
Authors: Ryu Sei Hyung , Krishnaswami Sumi , Das Mrinal K. , Richmond Jim , Agarwal Anant K. , Palmour John W. , Scofield James D.
Published: March 2009

Due to the high critical field in 4H-SiC, the drain charge and switching loss densities in a SiC power device are approximately 10X higher than that of a silicon device. However, for the same voltage and resistance ratings, the device area is much smaller for the 4H-SiC device. Therefore, the total drain charge and switching losses are much lower for the 4H-SiC power device. A 2.3 kV, 13.5 mW-cm2 4H-SiC power DMOSFET with a device area of 2.1 mm x 2.1 mm has been demonstrated. The device showed a stable avalanche at a drain bias of 2.3 kV, and an on-current of 5 A with a VGS of 20 V and a VDS of 2.6 V. Approximately an order of magnitude lower parasitic capacitance values, as compared to those of commercially available silicon power MOSFETs, were measured for the 4H-SiC power DMOSFET. This suggests that the 4H-SiC DMOSFET can provide an order
of magnitude improvement in switching performance in high speed switching applications.
4H-SiC Lateral RESURF MOSFETs on Carbon-Face Substrates
Authors: Okamoto Mitsuo , Suzuki Seiji , Kato Makoto , Yatsuo Tsutomu , Fukuda Kenji
Published: March 2009

We have fabricated lateral RESURF MOSFETs on 4H-SiC(0001) Si-face and (000-1) C-face substrates, and compared those properties. The channel mobility of a lateral test MOSFET on a C-face was 41 cm2/Vs, which was much higher than 5 cm2/Vs for that on a Si-face. The specific on-resistance of the lateral RESURF MOSFET on a C-face was improved to 79 mΩcm2 as comparison with 2400 mΩcm2 for Si-face. The breakdown voltage was 490V for Si-face and 460V
for C-face, which was 82% and 79% of the designed breakdown voltage of 600V, respectively. The device breakdown occurred destructively at the gate electrode edge.
Dose Designing for High-Voltage 4H-SiC RESURF MOSFETs - Device Simulation and Fabrication
Authors: Kawano H. , Kimoto Tsunenobu , Suda Jun , Matsunami Hiroyuki
Published: March 2009

Optimum dose designing for 4H-SiC (0001) two-zone RESURF MOSFETs is investigated by device simulation and fabrication. Simulated results suggest that negative charge at the SiC/SiO2 interface significantly influences breakdown voltage. Simulation has also showed that breakdown voltage strongly depends on LDD (Lightly-Doped Drain) dose. The dose dependencies of the breakdown voltage experimentally obtained are in good agreement with the device simulation. A
RESURF MOSFET, processed by N2O oxidation, with an optimized dose blocks 1080V and has a low on-resistance of 79 mcm2 at a gate oxide field of 3.0 MV/cm, which is the best 4H-SiC RESURF MOSFET ever reported.
High Field Effect Mobility in Si Face 4H-SiC MOSFET Made on Sublimation Grown Epitaxial Material
Authors: Sveinbjörnsson E.Ö. , Ólafsson H.Ö. , Gudjónsson G. , Allerstam Fredrik , Nilsson Per Åke , Syväjärvi Mikael , Yakimova Rositza , Hallin Christer , Rödle T. , Jos R.
Published: March 2009

We report on fabrication and characterization of n-channel Si face 4H-SiC
MOSFETs made using sublimation grown epitaxial material. Transistors made on this
material exhibit record-high peak field effect mobility of 208 cm2/Vs while reference
transistors made on a commercial epitaxial material grown by chemical vapor deposition (CVD) show field effect mobility of 125 cm2/Vs. The mobility enhancement is attributed to better surface morphology of the sublimation grown epitaxial layer.
A 4H-SiC BJT with an Epitaxially Regrown Extrinsic Base Layer
Authors: Danielsson Erik , Domeij Martin , Lee Hyung Seok , Zetterling Carl Mikael , Östling Mikael , Schöner Adolf , Hallin Christer
Published: March 2009

4H-SiC BJTs were fabricated using epitaxial regrowth instead of ion implantation to form a highly doped extrinsic base layer necessary for a good base ohmic contact. A remaining p+ regrowth spacer at the edge of the base-emitter junction is proposed to explain a low current gain of 6 for the BJTs. A breakdown voltage of 1000 V was obtained for devices with Al implanted JTE.
2-Inch 4H-SiC Homoepitaxial Layer Grown on On-Axis C-Face Substrate by CVD Method
Authors: Kojima Kazutoshi , Okumura Hajime , Kuroda Satoshi , Arai Kazuo , Ohi Akihiko , Akinaga Hiroyuki
Published: March 2009

Homoepitaxial growth was carried out on 4H-SiC on-axis substrate by horizontal hot wall chemical vapor deposition. By using carbon face substrate, specular surface morphology of a wide area of up to 80% of a 2-inch epitaxial wafer was obtained at a low C/Si ratio growth condition of 0.6. The Micropipe in on-axis substrate was indicated to be filled with spiral growth and to be dissociated into screw dislocations during epitaxial growth. It was found that the appearance of basal plane
dislocations on the epitaxial layer surface can be prevented by using an on-axis substrate.
Temperature Stability of Breakdown Voltage on SiC Power Schottky Diodes with Different Barrier Heights
Authors: Pierobon R. , Meneghesso G. , Zanoni E. , Roccaforte Fabrizio , La Via Francesco , Raineri Vito
Published: March 2009

The static and dynamic electrical characterization of power Schottky rectifiers both with Ti and Ni2Si as Schottky metals having low negative coefficient of the breakdown voltage versus temperature will be presented in this paper. The values of the barrier height are respectively 1.28eV and 1.68eV, as extracted using the Tung’s model for inhomogeneous contacts from forward currentvoltage
characteristics. These values were found to be in good agreement with those obtained by means of capacitance-voltage measurements. The breakdown voltage shows an almost linear dependence from the temperature for both types of devices. The extracted coefficients are respectively -0.08V/°C and -0.11V/°C, thus guarantying stable and reliable behaviour. Very short reverse recovery time at RT and at 125°C confirms the good thermal stability of these devices.
Temperature Dependence of 4H-SiC JBS and Schottky Diodes after High Temperature Treatment of Contact Metal
Authors: Pérez R. , Mestres Narcis , Tournier Dominique , Jordá Xavier , Godignon Philippe , Vellvehi Miquel
Published: March 2009

In this work we demonstrate performant characteristics of 1.2KV Schottky, Junction
Barrier Schottky (JBS) and implanted PN diodes processed on the same 4H-SiC wafer. A bi-layer Ni/Ti scheme for the contact metallisation submitted to high temperature rapid thermal anneals is proved to form good ohmic contact on p+ implanted areas while maintaining good Schottky characteristics on lightly doped n-type regions. I-V characteristics have been evaluated from room temperature up to 560K. At room temperature, Schottky diodes have slightly better specific onresistance, but when working temperature is increased, the JBS diode exhibits better characteristics due to the temperature dependent activation of bipolar current injection from the p+ grid. From reverse measurements, the JBS diodes showed lower leakage current and higher breakdown voltages in comparison to that of the Schottky diodes in the whole range of temperatures.
8.3 kV 4H-SiC PiN Diode on (000-1) C-Face with Small Forward Voltage Degradation
Authors: Nakayama Koji , Sugawara Yoshitaka , Tsuchida Hidekazu , Miyanagi Toshiyuki , Kamata Isaho , Nakamura Tomonori , Asano Katsunori , Ishii R.
Published: March 2009

The dependence of forward voltage degradation on crystal faces for 4H-SiC pin diodes has been investigated. The forward voltage degradation has been reduced by fabricating the diodes on the (000-1) C-face off-angled toward <11-20>. High-voltage 4H-SiC pin diodes on the (000-1) C-face with small forward voltage degradation have also been fabricated successfully. A high breakdown
voltage of 4.6 kV and DVf of 0.04 V were achieved for a (000-1) C-face pin diode. A 8.3 kV blocking performance, which is the highest voltage in the use of (000-1) C-face, is also demonstrated in 4H-SiC pin diode.
Large Area, Avalanche-Stable 4H-SiC PiN Diodes with VBR > 4.5 kV
Authors: Peters Dethard , Elpelt Rudolf , Schörner Reinhold , Dohnke Karl Otto , Friedrichs Peter , Stephani Dietrich
Published: March 2009

Large area 4H-SiC PIN diodes have been fabricated which exhibit a stable
avalanche ranging between 4.5 and 5.5 kV. The avalanche occurs at an electrical field strength of 2.1 MV/cm at the pn junction. The temperature coefficient of the avalanche is positive (0.3 V/K). The avalanche is tested in DC mode. The device concept as well as the fabrication process is described in detail. Static and dynamic characteristics are shown.
Friction Stir Welding of Dissimilar Formed Mg Alloys (AZ31/AZ91)
Authors: Lee Chang Yong , Lee Won Bae , Yeon Yun Mo , Jung Seung Boo
Published: March 2009

Friction stir welding of dissimilar formed Mg alloys(AZ31/AZ91) was successfully carried out at the limited welding conditions. In a sound joint, SZ was mainly consisted of AZ31 Mg alloy which was located the retreating side. Dynamic recrystallization and grain growth occurred and β intermetallic compounds of AZ 91 Mg alloy was not observed in SZ. BM had a higher hardness than that of the weld zone. The fracture location was not weld zone but BM of the AZ91 Mg alloy in tensile test.
Photocatalytic Behavior of Na2ZrTi5O13 Sol-Gel
Authors: Garza-Tovar Lorena L. , Torres-Martínez Leticia M. , Ramos-Garza J.S. , Castillo-Torres L.G.
Published: March 2009

The photocatalytic activity of samples of the new ceramic semiconductor, Na2ZrTi5O13 sol-gel, was studied using two different reactions, the decomposition (oxidation) of methylene blue and reduction-oxidation of Pb (II) from aqueous solutions at room temperature. We synthesised Na2Ti5ZrO13, which is isostructural to the family of compounds with general formula AnMTimO13, (A = Li, Na, K; M = Zr). These materials present a zig zag arrangement forming rectangular tunnels
in their structure. The synthesis of this compound was achieved by sol-gel technique using metalic alcoxides at two different pH, 3 and 9. The fresh gels were heat treated at 200°C, 400°C, 600°C and 800°C. The reaction products were characterized by X-ray diffraction (XRD), thermal analysis (DTA, TGA) and infrared spectroscopy (FTIR). The band gap energy (Eg) of each sample prepared was calculated from the UV-Vis absorption spectra. . The values of Eg obtained ranged from 3.5 to 3.2 eV. The best activity found for the methylene blue degradation was performed by the Na2ZrTi5O13 sol-gel pH 9, treated at 800oC (99%). We assumed that the photocatalytic activity is favored when the structure was already formed. Lead photocatalysed reactions using Na2ZrTi5O13
sol-gel pH 9, treated at 600 oC showed a higher eficiency (98%) than that obtained by TiO2 (degussa) (85%).
Microstructure and Mechanical Extruded Properties of Extruded AM50+xCa Magnesium Alloys
Authors: Wang Qu Dong , Peng Jianguo , Liu Man Ping , Chen Yongjun , Ding Wen Jiang , Suéry Michel , Blandin Jean Jacques
Published: March 2009

As-cast AM50 magnesium alloys containing 0, 1, 2 wt. %Ca were extruded firstly at 673K with an extrusion ratio 1:9, and then at 573K with an extrusion ratio 1:16. Microstructure, tensile properties and fractographs were investigated. With Ca content increasing, the amount of Al2Ca increases and that of Mg17Al12 decreases. Ca refines the microstructure of as-cast and extruded AM50 magnesium alloys. For the extruded magnesium alloys, tensile strength improved and elongation decreased at room temperature, while tensile strength was reduced a little and elongation
reduced at the temperature of 100°C, 150°C and 200°C with increasing Ca content. The tearing face increases with Ca content increasing for the tensile fractographs.
Effects of Nd on the Microstructure and Mechanical Property of ZA52 Alloy
Authors: Zou Honghui , Zeng Xiao Qin , Zhai Chun Quan , Ding Wen Jiang
Published: March 2009

Microstructure and mechanical property changes brought by the addition of Nd element in Mg-5wt%Zn-2wt%Al alloy are investigated, results show Al element takes a priority to react with Nd element over Mg and Zn, forming binary phases Al2Nd or Al11Nd3, tensile test showed that the total elongation is improved by the addition of Nd, and the UTS is also elevated when the Nd content surpass 1wt%. With a larger Nd addition, the phase dominating grain boundary is Al11Nd3 phase.
First-Principles Investigation of Laves Phases in Mg-Al-Ca System
Authors: Zhong Yu , Luo Alan A. , Sofo Jorge O. , Liu Zi Kui
Published: March 2009

Recent experiments and first-principles calculations in the literature revealed the existence of a C36 laves phase in the Al2Ca-Mg2Ca pseudo-binary system in addition to the C14-Mg2Ca and C15-Al2Ca laves phases. In the present work, special quasirandom structures (SQS) for all three laves phases were constructed. The structures possess local pair and multisite correlation functions
that mimic those of the corresponding random structures. First-principles calculations were carried out based on the SQS developed to predict the enthalpy of formation in the Al2Ca-Mg2Ca pseudo-binary system. It was observed that the enthalpy of formation of C36 is very close to that of C14 at the Mg2Ca end and decreases with the addition of small amount of Al, while the enthalpy of formation of C14 increases with the addition of Al. It is thus energetically plausible that C36 is
stable in the Al2C- Mg2Ca pseudo-binary system.
Fabrication of Bulk Amorphous Mg65Cu25Gd10 Alloy of 12mm Rod by Water Quenching
Authors: Liu W.Y. , Zhang Haifeng , Hu Zhuang Qi , Wang H. , Yao X.D.
Published: March 2009

Bulk armorphous Mg65Cu25Gd10 alloy of 12mm rods were prepared by water quenching the molten alloy in the stainless steel tube. Neither cavities nor voids are seen over the whole range and no contrast revealing a crystalline phase is seen over the transverse cross section. The glass transition temperature (Tg), crystallization temperature (Tx), the melting temperature (Tm) and the
liquidus temperature (Tl) are measured to be 419K, 492K, 702K, 735K, respectively, for the Mg65Cu25Gd10 alloy with a diameter of 12mm. These temperatures are similar with those of the alloy with a diameter of 8mm produced by metallic mould casting. Both alloys have the same Vickers hardness about 260. Water quenching can further improve the critical diameter of glassy rods, so it is qualified for the formation of the bulk alloys.
Microstructure Evolution of Mg-Y-Nd-Zr Alloy during High Temperature Deformation
Authors: Tang Wei Neng , Chen Rongshi , Han En-Hou
Published: March 2009

The variation of the flow stress and the microstructural evolution during hot deformation at different test temperatures and strain-rates are studied. During hot deformation, dynamical recrystallization did not occur completely; after annealing at 523K, microstructural changes due to static recrystallization and small grain sizes of several micrometers and fine nanometer-precipitates can be attained. The stress exponent (n) and the activation energy (Q) for high temperature deformation have been evaluated and the deformation mechanisms at different temperature have also been discussed.
On some Characteristics of Microstructure and Defects in Die-Cast Magnesium Components
Authors: Cao Hai Ping
Published: March 2009

Some commercial Mg components have been die cast at various casting conditions. The influence of process parameter settings on the microstructural features as well as one kind of defect called segregation band defect were investigated. It was found that more pre-solidified crystals were formed in the condition of lower casting temperature, and more broken dendrites and spherical crystals were formed under higher injection speed. The distribution characters of pre-solidified crystals were also presented and discussed in this paper. Concerning the band defects formed during die casting, a variety of segregation band morphologies as well as the influence of various casting conditions the performances on bands was presented. It was found out that intensification pressure has the strongest effect on the performance of segregation bands inside the castings.
Semi-Solid Processing Technologies of Magnesium Alloys
Authors: Li Xing Gang , Xie Shui Sheng , Jiang Yun Xi , Li Lei
Published: March 2009

Magnesium alloys are becoming more and more attractive because of their low density, high specific stiffness and strength, good heat conductivity, high electromagnetic interference shielding and damping capabilities, etc. Magnesium alloy components produced by semi-solid processing (SSP) has the merits of high dimension stability and quality. Moreover, it is desirable to apply the SSP technology to produce components free of gas holes and porosity which are usually
found in those produced by the die casting. SSP of magnesium alloys has been utilized in Japan and Taiwan, China. In this paper, preparing methods of semi solid slurry appropriate for magnesium alloys are introduced, including stirring, SSIT-semi solid isothermal heat treatment, pouring temperature controlling, grain refinement and so on. The effects of process parameters on the microstructure of semi-solid slurry are also discussed. In addition, thixomolding technology practically utilized in the semi-solid processing of magnesium alloys is also introduced. At last the prospect of Semi-solid processing technologies for magnesium alloys are discussed.
The Microstructures of As-Cast Mg-Zr and Mg-Mn Alloys
Authors: Li Jian Ping , Lorimer Gordon W. , Robson Joseph D. , Davis B.
Published: March 2009

The as-cast microstructures of two dilute Mg-Zr and three dilute Mg-Mn alloys were
studied using optical microscopy and scanning electron microscopy, including EDX analysis. The results show that the as-cast microstructure of the Mg-Zr alloys was composed of non-dendritic, equiaxed Mg grains, with a few Zr particles within the Mg grains and along grain boundaries. The grain size of the Mg-Zr alloy was significantly reduced by the Zr addition and a fine grain structure was achieved when the zirconium concentration was above 0.4wt. %. The as-cast structure of the
Mg- Mn alloys contained columnar, dendritic grains. Two types of Mn particles (equiaxed large particles and rod-like or plate-like small particles) were observed in the as-cast Mg-Mn alloys. The volume fraction of particles and the size differences between the large and small particles increased with an increase of Mn concentration.
Influence of Process Conditions of Thixomolding® on the Microstructure of Magnesium Mobile Phone Housing
Authors: Cui Xiao Peng , Liu Yong Bing , Cao Zhan Yi , Yang Xiao Hong , Liang Wei
Published: March 2009

Thixomolding® is a new process of net shape parts for magnesium alloys in one step, and it is suited to manufacture the thin wall products, especially to the electronic component shells. In this paper, the sample of mobile phone housing is fabricated by 220Tons Thixomolding® machine made by Japan Steel Works. The effects of barrel temperature, screw rotate rate and mold temperature on microstructure were studied. The relationship between process parameters and
microstructure was also discussed in this paper.
Theoretical Analysis of Plastic Forming Process for Semi-Solid Material
Authors: Yan Hong , Xei Juchen
Published: March 2009

The plastic forming of magnesium alloy is difficult, but the semi-solid material forming
is a good method solved this problem. The mechanical model of the semi-solid materials was treated as that of the continuous porous materials in the high solid volume fraction. The upper bound theory applied for semi-solid metal plastic forming process was developed. The velocity discontinuities exist not only in the tangential component but also in normal component for the kinematically admissible displacement increment filed. The latter one was responsible for a change in solid volume fraction when the material passes the discontinuity. An upper bound analytical model and theoretical method of plastic forming process for semi-solid material has been proposed. The calculating formulas of deformed power were derived. It is theoretical basement to apply further for the practice technology analysis such as the plastic forming of magnesium alloy.
Manufacturing and Application of Continuous Cast Semi-Solid Processed Magnesium Alloys
Authors: Jung Hwa Chul , Kim Ye Sik , Shin Kwang Seon
Published: March 2009

The demand for magnesium alloys has increased significantly during the past decade in the automotive and electronic industries where weight reduction becomes increasingly an important issue. At present, high-pressure die casting (HPDC) is a dominant process in production of magnesium alloy components. However, magnesium alloy components produced by HPDC suffer from porosity problem and this limits the enhancement of mechanical properties through subsequent heat treatments. The semi-solid processing (SSP) is an emerging new technology for near-net shape production of engineering components, in which the alloys are processed in the temperature range where the liquid and solid phases coexist. The SSP has various advantages over the conventional casting processes. It offers the castings with high integrity and less porosity and allows subsequent heat treatments for enhancement of mechanical properties. For these advantages, the SSP of
magnesium alloys has received increasing attention in recent years. In the present study, the continuous casting process was developed for the production of magnesium billets for the subsequent SSP. The process utilizes an electromagnetic stirring system in order to obtain desired microstructure with an excellent degree of homogeneity in both microstructure and composition. Prototypes of an air conditioner cover and a telescope housing were produced using the SSP of the continuously cast magnesium alloy billets.
Development of Strip Casting Process for Fabrication of Wrought Mg Alloys
Authors: Park Sung S. , Kang Dae H. , Bae Geun Tae , Kim Nack
Published: March 2009

AZ31 and experimental ZMA611 alloys were strip cast into 2 mm thick strips. The as-cast AZ31 alloy strip consists of columnar dendrites. On the other hand, as-cast ZMA611 alloy strip shows equiaxed dendritic structure through the thickness of strip. Strip cast AZ31 alloy in H24 condition has equivalent yield and tensile strengths with similar ductility compared to commercial ingot cast AZ31-H24 alloy, indicating that strip casting is a viable process for the fabrication of Mg alloy strips.
The ZMA611 alloy has a large volume fraction of fine dispersoid particles in the microstructure, resulting from the beneficial effect of strip casting on microstructural refinement. It has been shown that the ZMA611 alloy has superior tensile properties compared to commercial ingot cast AZ31-H24 alloy, suggesting the possibility of the development of new wrought Mg alloy sheets by strip casting.
Manufacturing Technique of Magnesium Alloy Sheets by Powder Rolling
Authors: Huang Guang Sheng , Wang Ling Yun , Zhang Zhong Wei , Huang Guang Jie , Pan Fu Sheng
Published: March 2009

Conventional manufacturing processes of metal and alloys sheets are rolling. The poor formability of magnesium alloys at room temperature makes rolling difficult. In the present paper, a manufacturing technique of sheets by powder rolling was employed to fabricate magnesium alloy sheets. The technique consisted of roll compaction, sintering, re-rolling and annealing. Powders of Mg-3 wt% Al mixed using a global mill were roll compacted into green sheets using two counter rotating rolls to the thickness of approximately 0.60 mm. Roll compacted green sheets were sintered
at 823 K in argon atmosphere. Sintered green sheets were then re-rolled at ambient temperature to approximately 0.22 mm to obtain fully dense sheets. There was no significant edge cracking observed in the process of cold rolling. It is reasonable to believe that powder rolling is a promising technique for manufacturing magnesium alloys sheets.
Finite Element Analysis of Press Forging Process of AZ31 Sheet
Authors: Hwang Jong Kwan , Sohn Keun Yong , Kang Dae Min , Shin Young Su
Published: March 2009

In this paper, the distribution of temperatures on specimen and the variations in punch forces on friction coefficients during press forging of AZ31 sheets have been analyzed by Finite Element Analysis technique. Results show that the top of rib and boss areas showed lower temperatures than other areas because of the heat dissipation to air by radiation. The foot regions of the rib and boss showed greater temperature rise due to greater plastic flow. The applied punch force significantly increased at 473K or lower temperatures indicating the forming temperature of AZ31
sheet should not lower than 473K. The friction condition of the punch influenced more significantly on the materials flow pattern compared to those of the die. Using a lubricant on the contact area between the punch and specimen would effectively reduce the punch force and enhance the forming capability.
Improved Formability and Deep Drawing of Cross-Rolled Magnesium Alloy Sheets at Elevated Temperatures
Authors: Xu Yong Chao , Zhang Shi Hong , Liu H.M. , Wang Z.T. , Zheng W.T. , Zhang Q.L. , Xu Y.
Published: March 2009

The extruded sheets were prepared at the temperature between 350ıand 400ı, and the magnesium alloy sheet was manufactured by a new method, cross rolling, in which the rolling direction was changed in each pass. At the time, deep drawing of magnesium alloy sheet was investigated at elevated temperatures. The results show that the sheet has refined-grain by cross-rolling after it was annealed at 250ı, and the formability is significantly improved at lower temperatures, which is superior to the extruded sheet and the one-way rolled sheet. Deep drawing of magnesium alloy was performed successfully, and cylindrical cup of limited drawing ratio (LDR) 2.6
and 35 mm deep rectangular box (65ı50) was achieved at the lower temperature of 170ı. The different types of fracture were analyzed and reasonable parameters were determined.
Management and Recycle of Magnesium Alloy Scraps in Die Casting Factory
Authors: Tseng Kun-San , Sheu Guang-Liang , Huang Shih Tsung
Published: March 2009

Up to date, a reasonable and adequate process to treat magnesium scraps in die casting factory is not yet achieved, especially for middle or small scale die casters. Actually, many existing methods of handling magnesium scraps have met the level of technology for practical utilization requirement. Now, what we have to do is to propose a systematic handling process according to factory suitability and cost consideration. In this paper, the classification of magnesium scraps will be introduced first. Then the complementary storage methods and treatment methods for each type of scraps and recycle policy for die casters will be discussed. Finally, we propose a management model of magnesium scraps that is possibly suitable to some die casting factories.
Investigation on Deformation in ZK60 at High Strain Rate
Authors: Zhang Xing , Li Bao Cheng , Zhang Zhi Min , Wang Zhi Wen
Published: March 2009

Split Hopkinson Pressure Bars (SHPB) was applied to investigate shock resistance of magnesium alloy. The deformation behaviour was reported of ZK60 magnesium alloy at high strain rate, and the relationship was established between the dynamic properties and the impact velocity. Results indicate: with impact velocity improvement, much twinned crystal and fine grain can be obtianed, this made dynamic properties enhancement of ZK60 alloy.
Forming Limit and Loading Path of Mg-Alloy Tube Bulging
Authors: Liu Gang , Jäger Stephan , Siegert Klaus
Published: March 2009

The paper researched formability ability of AZ31 Mg-alloy tube by hot pneumatic
bulging. FEM simulations were carried out to reveal the effect of internal pressure changing on bulging process and forming limit. Several loading paths with different pressure changing were used in the simulations. From the research, the original expansion ratio of diameter using a bilinear loading path, namely the internal pressure was increased linearly, is only 22%, and bursting occurs quickly. With a step-like loading path, namely the internal pressure is increased step by step, among
the steps, the pressure is kept constant, and the strain rate of bulging can be kept into a small range. Thus the deformation around the hoop direction is more even than the linear loading path, and than bursting can be postponed. During bulging, the inner pressure should be lowered with the increase of diameter to keep the strain rate in a small range around a constant value. Through optimization of loading path, the forming limit can be enhanced obviously so that the expansion ratio of diameter
can be increased to 25.1%.
Metal Quality - From Ingot to Finished Product
Authors: Bakke Per , Andersen Per Kristian , Svalestuen Jørild M. , Strømhaug Svenn Ivar
Published: March 2009

Optimum performance of metal in the die casting shop in terms of metal loss, sludge
generation, and high quality and consistency in mechanical properties of the die cast components are becoming increasingly important. In this context metal quality both from alloy producers’, die casters’ and end users’ perspectives is critical. The term metal quality can be defined to include 1) chemical composition, 2) inclusions and porosity inside the metal, 3) the surface appearance, and 4) consistency. This definition may apply to ingots as well as die cast parts. When the ingots are
remelted and processed in the die casting shop, the effect of ingot surface quality and porosity on performance and properties is usually overshadowed by the quality of the processes in the die casting furnace. The paper discusses how the alloy gradually loses its pre-history. If the metal quality becomes inferior, housekeeping may become notoriously difficult, affecting important performance indicators such as up-time of operation and scrap rate. In partnership with the individual die casters, Hydro Magnesium offers assistance and audits to further improve the die caster’s performance and products.
Properties of Conversion Coating of Magnesium Alloys by a Phosphate-Permanganate Solution
Authors: Wu Shu Sen , Zhao Ming , Luo Ji Rong , Mao You Wu
Published: March 2009

A chromium-free conversion coating for AZ91D magnesium alloys has been obtained by using a phosphate-permanganate solution. Examinations have been carried out on the conversion coating for morphology, composition, adhesion force and corrosion resistance. Results show that the conversion coatings are relatively uniform and continuous, with thickness from 7µm to 10µm. They exhibit good adhesion to matrix and have some non-penetrate tiny holes on the surface. The
main elements of the conversion coating of AZ91D alloy are Mg、O、P、K、Al、Mn. Results of corrosion resistance test indicate that the corrosion resistance of the conversion coating by phosphate-permanganate solution is in match to that of the conversion coating formed in a chromate solution, but for the corrosion resistance after painting, the former is better than the later.
Al Arc Spray Coating on AZ31 Mg Alloy and Its Corrosion Behavior
Authors: Wei Zhong Shan , Liu Liufa , Ding Wen Jiang
Published: March 2009

Aluminum arc spray process was employed to form an aluminum coating on AZ31
magnesium alloy substrate. Anti-corrosion property of the Al-coated specimens was evaluated by salt immersion tests and electrochemical tests. There was no apparent inter-layer diffusion or compound layer formation between the aluminum coating and the substrate under as-sprayed condition. To improve the density of the coating and the bonding strength between the coating and the substrate, a heat treatment process was conducted after spraying to form an interlayer by metallurgic diffusion. The interlayer consisted of large primary crystal Mg17Al12 phase and minute lamella structure that consisted of Mg17Al12 and α-Mg. The hardness of both the aluminum coating and the interlayer are higher than that of the substrate. In electrochemical experiments, the corrosion current density decreased from 2.4×10-1mA/cm2 of AZ31 to 7.1×10-3mA/cm2 of heat-treated specimen. It suggests that the corrosion resistance of AZ31 can be greatly improved by aluminum arc spray with a following heat treatment process.
Structural Characteristics and Electrochemical Properties of Mg-Ni-Cu-Y Alloy Synthesized by Mechanical Alloying
Authors: Wang Li Min , Zhang Xin Bo , Wu Yao Ming
Published: March 2009

A powder material of Mg-Ni-Cu-Y was synthesized by mechanical alloying method.
Considerable amounts of amorphous and nanocrystalline phases formed after a mixture of elemental powder with the overall composition of Mg78Ni9Cu11Y2 was mechanical alloyed for 200 h. The phase formed in the synthesized powder materials was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The electrochemical properties were examined with a solution of 6M KOH.
Effect of Pulsed High Energy Ion Beam on Surface Modification of AZ91 Magnesium Alloy
Authors: Zhao Hui , Han Zhong , Liu Zhen
Published: March 2009

This study is concerned with the effect of high energy ion beam irradiation on surface
properties of AZ91 magnesium alloy. The study included a characterization of ion beam surface modification zone in terms of microstructure, and mechanical properties like nanohardness, wear, and corrosion resistance of the surface layer were studied in details. Nanohardness of the modification layer was improved about 2 times as that of the as-received AZ91. The corrosion resistance of the modified layer was significantly improved in NaCl solution because of refined grains. The wear
resistance of the modification layer was also improved as compared to as-received AZ91.
High-Temperature Mechanical Properties of As-Extruded ZK60
Authors: Wu Wei , Hong C.M. , Chen Li Jia , Wang Yue , Yang Lin , Li Feng , Liu Zhen
Published: March 2009

High-temperature tensile and fracture behaviors of as-extruded ZK60 alloy were
investigated. It was evident from the experiments that with decreasing temperature and increasing strain rate, the 0.2% offset yield strength and ultimate tensile strength of the alloy increased while the elongation to failure decreased. The flowing stress of as-extruded ZK60 alloy during plastic deformation was proportioned to the reciprocal of temperature. At the initial strain rate of 5×10-4s-1, the calculated active energy at 300°C was about 93.4 kJ/mol.
A Novel Technique for On-Line Generation of Mg-Shielding Gas
Authors: You Guo Qiang , Long Si Yuan , Zha Jili
Published: March 2009

A new technique capable of on-line generating SO2+CO2+N2 shielding gas via thermal chemical reaction between compressed air and a mixture of C and S powder was introduced in the present study. The test results in both laboratory and foundry indicate that the on-line generated gas is able to provide effective protection to Mg melting bath up to 730 oC as SF6+N2 shielding gas does, while its running cost is 30% less than of the latter.
Deformation Behavior of Polycrystalline AZ31 Alloy at Room and Elevated Temperatures
Authors: Zhou Tsing , Itoh Goroh , Iseno Yohei , Motohashi Yoshinobu
Published: March 2009

The hot-rolled and extruded AZ31 specimens are subjected to tensile tests at room and elevated temperatures. At room temperature, the yield stress of the hot-rolled specimen is significantly higher than that of the extruded, the reason for which is related to the different textures developed in the two type specimens, as well as the different slip systems activated. At elevated temperatures, the strain rate sensitivity and the activation energy are obtained to characterize the deformation mechanism of the alloy during the temperature range of 423~573K.
Compressive Deformation Behavior of the SiCw/AZ91 Composite at Elevated Temperatures
Authors: Li S.B. , Gan Wei Min , Zheng Ming Yi , Wu Kun
Published: March 2009

Compressive behaviors of SiCw/AZ91composite and AZ91 alloy were investigated at
temperatures from 423 K to 723 K and strain rates from 0.002 s-1 to 0.25 s-1. Microstructure evolutions after compressed at 623 K and 0.01 s-1 were observed by SEM and TEM. Results showed that compressive flow stress decreased with the increase of temperature; whiskers were broken and redistributed to the direction normal to the compression direction. At the initial stage of compression, dislocation sliding is the mainly deformation mode for the composite, while for AZ91 alloy, twining was the dominant mechanism.
Protection of Mg Alloys against Galvanic and Other Forms of Corrosion
Authors: Zheng Wen Yue , Derushie C. , Lo Jason
Published: March 2009

Galvanic corrosion is a particularly important form of corrosion for Mg alloys used in
automobiles. Our research work focuses on corrosion protection using cost-effective Cr-free coatings. The top-tanking coatings are found to be effective in preventing general corrosion; some of these coatings are also good for reducing galvanic corrosion and stress corrosion. A practical approach for mitigating galvanic corrosion is to increase the electrolytic resistance between the coated steel and the Mg surfaces. This has been demonstrated in the case of a conversion coating plus a powder coat applied on the surface of a magnesium alloy and in the case of a thin Mylar isolation layer installed between the Mg and the steel surfaces.
Electrochemical Behavior of Magnesium and Aluminium Ions in Alkali Chloride Melt
Authors: Zhang Xi , Jiao Shuqiang , Xiao Saijun , Zhu Hong Min
Published: March 2009

The electrodeposition of aluminium and magnesium in lithium chloride-sodium chloride
(mass 5:1) melt at 700°C has been studied using cyclic voltammetry, square wave voltammetry and chronopotentiometry. The reduction of aluminium and magnesium ions on tungsten electrode are both reversible processes, with three and two electrons exchanged: Al3++3e → Al, Mg2++2e →Mg. The diffusion coefficients of Al3+ and Mg2+ were determined as 2.72×10-5 cm2 s-1 and 1.58×10-4cm2 s-1 respectively. A laboratory test of the direct production for the Mg-Al alloy was performed to show the feasibility of electrochemical co-deposition of magnesium base alloys.
Characterization of Wear and Corrosion Protective Coatings Formed on AZ91 Magnesium Alloy and SiCw/AZ91 Magnesium Matrix Composite by Microarc Oxidation
Authors: Wang Y.Q. , Zheng Ming Yi , Wu Kun
Published: March 2009

The wear and corrosion protective coatings were synthesized on AZ91 Mg alloy and Mg matrix SiCw/AZ91 composite by a microarc oxidation (MAO) technique in an alkali-silicate electrolyte solution. The phase structure of the coatings was analyzed using X-ray diffraction (XRD). The tribological properties of the coatings sliding against GCr15 steel were investigated on a pin-on-disc friction and wear tester. The morphology and elemental composition of the worn coating surface were determined by scanning electron microscopy (SEM) and energy dispersive
spectrometer (EDS). The potentiodynamic polarizing curves were measured to evaluate the corrosion resistance of the coatings. The results showed that the application of the coatings changed evolution tendency of friction coefficients and wear mechanism. For coated Mg alloy and Mg matrix composite, both the wear resistance and corrosion resistance were improved greatly.
Residual Stresses Measurement Using an Indentation Made by an Impact Load
Authors: Lin Quan Hong , Chen Huaining , Chen Jing , Liang Yue
Published: March 2009

The impact-indentation stress measurement method makes use of the principle of superposition stress fields resulting from the residual stresses and the surface plastic deformation. The main laws measuring stress by impact-indentation method are that, in the direction of major stress, the strain increment is in direct proportion to major residual strain in same indentation sizes and the strain increment in the fixed distance from center of indentation is in direct proportion to indentation size in the
same residual stress fields. The stress measuring equipment has been developed and has more advantages than the hole-drilling method, such as higher precision, nondestructive, more convenient and rapid in the measuring process. Generally, its measurement error is less than 15 MPa. It has successfully applied in measuring residual stresses of various welded structures in the field.
Neutron Evaluation of Stress in Industrial Screws
Authors: Fabre Agnès , Lillamand Ivan , Masse Jean-Éric , Barrallier Laurent
Published: March 2009

Neutron diffraction measurements were used in this study in order to determine the axial stress state in loaded screw from a specific assembly. The knowing of stress gradient is need to qualify a standard gauge used to calibrate the response of in-situ measurements using ultrasonic nondestructive technique. US is well adapted to perform measurements of the evolution of stress state on industrial screws during service life of the bolded assemblies.
An Investigation of Residual Stress of Porous Titania Layer by Micro-Arc Oxidation under Different Voltages
Authors: Huang Ping , Xu Ke Wei , He Bob B. , Han Yong
Published: March 2009

The surface modification of titanium by micro-arc oxidation under different voltages was processed to achieve good direct oseointegration. The new technique of two-dimensional X-ray diffraction was used to measure the residual stress of the layer. The results show that a porous titania layer containing Ca and P is obtained by micro-arc oxidation. The pore size and Ca/P of the layer are affected by the voltage. The high voltage can induce forming CaTiO3. The residual stress under different voltage is compressive stress and increases with the improvement of the voltage.
3-D Finite Element Simulation of Welding Residual Stresses in Pipe-Flange Joints: Effect of Welding Parameters
Authors: Siddique M. , Abid Muhammad , Junejo H.F. , Mufti R.A.
Published: March 2009

This paper presents results of detailed three-dimensional finite element simulation of
residual stress distribution in welded Pipe-Flange Joints with emphasis on the effect of welding parameters and geometrical size of the model. Single-pass Metal Inert Gas welding with single “V” Butt-weld geometry is used in the study. The effect of two basic welding parameters including welding current and speed and two geometrical parameters i.e. pipe diameter and wall-thickness are examined. For both welding current and welding speed, three sets of parameters comprising of low, medium and high values are used. To analyze the effect of each parameter explicitly only one parameter is changed at one time. In most of the cases 100 mm nominal pipe diameter is used. A FE Model for 200 mm nominal pipe diameter is also analyzed to determine the effect of pipe diameter.