Mechanical Engineering
Materials Science & Engineering

ASM Materials Conference and Exposition

September 16-20, 2007

Heat Treating Society

The conference held in Detroit, Michigan was attended by Graduate Students: Xiaoshu Dai, Olga Karabelchtchikova, Radah Purushothaman, Tracey Vincent; Prof. Diran Apelian, Prof. Diana Lados, Prof. Richard Sisson, Jr., and Research Prof. Md. Maniruzzaman

Papers presented:

WPI Professor Richard Sisson Elected President of ASM Heat Treating Society

Richard D. Sisson Jr., George F. Fuller Professor of Mechanical Engineering at Worcester Polytechnic Institute (WPI) and director of the university's Manufacturing and Materials Engineering programs, has been elected president of the ASM Heat Treating Society (HTS), an affiliate society of ASM International, The Materials Information Society. The meeting took place in Detroit, MI on September 18, 2007 during the ASM Materials Conference.

Thermodynamic and Kinetic Aspects of Endothermic Carburizing Atmospheres with Natural Gas Enrichment

Authors:

O. Karabelchtchikova, Center for Heat Treating Excellence
S.A. Jonston
H.F.M. DaCosta, Catapillar
R.D. Sisson, Jr., Center for Heat Treating Excellence

Abstract

Atmosphere gas carburizing is an essential heat treatment process used in industry. High carburizing potential in the furnace atmosphere enables a carbon flux from the atmosphere to the steel surface and across the gas-solid interface. This establishes a carbon gradient in the steel and provides a driving force for carbon diffusion into the bulk of the material. The goal of this work is to understand the effect of the enriching gas flow rate, and therefore, mean residence time, on the atmosphere carburizing potential. A thermodynamic model has been developed and programmed in MATLAB to predict equilibrium gas composition of both endothermic carrier gas and carburizing atmosphere during natural gas enrichment. The evolution of the concentrations of various gas species in the carburizing atmosphere has also been simulated with kinetic modeling implemented within COMSOL Reaction Engineering Lab. The predicted profiles show good agreement with the experimental data and can further be used to perform "what if" scenarios.

Fluidized Bed: An Energy Efficient Heat Treating Technology For Cast Al Alloys

Authors

D. Apelian
S. K. Chaudhury, WPI, Worcester, MA;
J. S. Keist, Arizotah, LLC, Plymouth, MN

Abstract

Post solidification heat treatment of cast Al alloys is often required to improve mechanical properties and better microstructural control. The heat treat cycle consists of a solution treatment, followed by quenching and an aging step. These heat treating steps may require several hours using conventional air resistance furnaces and contribute a substantial increment to the overall manufacturing cost. The major constraint to production flow in manufacturing operations using conventional furnaces arises from its labor intensive batch processing method; the relatively slow heating rate gives rise to cycle times in the range of 10-15 hours. Fluidized bed heat treating offers a more efficient means of energy transfer compared to conventional electric resistance furnaces and thus provides an energy efficient heat treating method. High heating rate of castings in fluidized bed is due to forced convectional heating. The high thermal mass of the bed material in fluidized bed ensures rapid and uniform heating of castings. In this paper, we will review the fundamentals of fluidized bed, highlight their advantages and examine applications and limitations of fluidized bed to heat treat cast Al alloys. Mechanical properties data along with the resultant microstructure as a result of extensive trials with fluidized bed technology will be presented, reviewed and discussed.

Fluidized Bed Quenching Performance and its Application for Heat Treating Aluminum Alloys

Authors

J. S. Keist, Arizotah, LLC, Plymouth, MN
S. K. Chaudhury
D. Apelian, WPI, Worcester, MA

Abstract

Fluidized bed quenching is an attractive alternative to liquid quenching processes since the part does not develop a vapor barrier during quenching. This lack of a vapor barrier significantly reduces residual stresses and part distortion that often plagues liquid based quenching techniques. The heat transfer rate of the quenching process, however, is lower than can be obtained by liquid based quenchants. The lower heat transfer rate may rule out fluidized bed quenching for some applications due to part geometry or alloy quench sensitivity. In this research, the heat transfer characteristics of the fluidized bed process were measured. The heat transfer characteristics was then utilized in computer modeling to develop a precise method for determining the applicability of fluidized bed quenching for aluminum parts of a given geometry and alloy.
Summary: A critical analysis of fluidized bed quenching and its potential applications in aluminum heat treating. This work includes analysis of the quenching characteristics of the fluidized bed process and an illustration is given on how modeling may be utilized to determine the expected quenching performance of the fluidized bed in regards to part geometry and alloy type.

Microstructure and Property Predictions by Using a Heat-Treatment Planning System, CHT-q/t

Authors:

L. Zhang
Y.M. Rong
R. Purushothaman
J.W. Kang, Tsinghua University

Abstract

Steel quenching is a heat treatment operation which results in the change of the microstructure and properties. In this paper, this process is modeled and simulated with an self-developed analytical tool, "Computerized Heat Treating and Planning System for Quenching and Tempering", i.e., CHT-q/t, which is to predict the temperature profile of load in batch as well as continuous furnaces during heating, quenching and tempering of steels, then to provide information about the mechanical properties as quenched. The system can be also used to optimize the heat treatment process design with the aim to save energy and reduce cost. The microstructure/phase transformation is predicted by solving Avrami-Johnson-Mehl equations through comparing cooling curves against materials TTT diagrams. The hardness of the workpiece is estimated as a distribution of the load, by considering the contribution of microstructure and carbon contents. The results are verified through running JOMINY end-quench harden ability tests. The calculation is a combination of numerical simulation and empirical equations. This tool is suitable for commercial and captive heat treaters for quality control and process optimization.

Evaluation of Aging Response of Al-Cu-Mg-Si Based Cast Aluminum Alloy and its Effect on Tensile Property

Authors:

M. Maniruzzaman
E. Wallhagen
R.D. Sisson, Jr.

Abstract

Aging of aluminum alloys is done to improve the alloy strength and other mechanical properties. The strengthening mechanism during aging is the nucleation of various precipitates and their growth, which primarily depends on the cooling rate, aging time and temperature as well as the alloy composition. In this study several 319 based (Al-Cu-Mg-Si) cast aluminum alloys are used to investigate the aging response of these alloys. A series of tensile tests is performed to determine the yield and tensile strengths of the alloy aged at selected aging temperatures and times. The effects of Cu and Mg concentrations on the aging response of the alloy are also presented and discussed.
Summary: Aging of aluminum alloys is done to improve the alloy strength and other mechanical properties. The strengthening mechanism during aging is the nucleation of various precipitates and their growth, which primarily depends on the cooling rate, aging time and temperature as well as the alloy composition. In this study several 319 based (Al-Cu-Mg-Si) cast aluminum alloys are used to investigate the aging response of these alloys. A series of tensile tests is performed to determine the yield and tensile strengths of the alloy aged at selected aging temperatures and times. The effects of Cu and Mg concentrations on the aging response of the alloy are also presented and discussed.

The Aging Behavior of AA7136 Wrought Aluminum Alloy

Authors

M. Maniruzzaman
C. Nowill
R. D. Sisson, Worcester Polytechnic Institute, Worcester, MA
D. S. MacKenzie, Houghton International, Inc., Valley Forge, PA

Abstract

The 7136 wrought aluminum alloy is an Al-Zn-Mg-Cu-Zr alloy, primarily used in the aerospace industry as structural components. This alloy is strengthened primarily by age-hardening. Limited data for the aging kinetics of this alloy is available in the literature. A series of Jominy end-quench tests were performed to investigate the effect of solutionizing temperature and cooling rate on the aging performance of the alloy. The process variables used in the study are solutionizing temperature and aging time. Quench factor analysis (QFA) has successfully been used over the years by various researchers to predict the physical properties of age-hardenable aluminum alloys. In this study, the Jominy end-quench data is used to determine the kinetic parameters for QFA. Time-temperature-property or "C" curve is also presented for this alloy.
Summary: The 7136 wrought aluminum alloy is an Al-Zn-Mg-Cu-Zr alloy, primarily used in the aerospace industry as structural components. This alloy is strengthened primarily by age-hardening. Limited data for the aging kinetics of this alloy is available in the literature. A series of Jominy end-quench tests were performed to investigate the effect of solutionizing temperature and cooling rate on the aging performance of the alloy. The process variables used in the study are solutionizing temperature and aging time. Quench factor analysis (QFA) has successfully been used over the years by various researchers to predict the physical properties of age-hardenable aluminum alloys. In this study, the Jominy end-quench data is used to determine the kinetic parameters for QFA. Time-temperature-property or "C" curve is also presented for this alloy.

The Role of Cleaning in Heat Treatment Process

Authors

X. Wang
M. Maniruzzaman
Y. Rong
R. D. Sisson,Jr.

Abstract

Surface contamination during heat treatment process can greatly affect the quality of the end products. Although cleaning the post heat treated parts is considered a value added process in heat treatment, pre heat treated parts cleaning is also important and can influence the outcomes of subsequent processes dramatically. Heat treatment industries are also facing growing challenges for replacing environmentally unfriendly cleaning chemicals and processes due to their concern for the environment as well as government regulations. This paper will discuss and characterize the surface contaminants which affect the various heat treatment processes and will identify the cleaning processes and the chemistries that are currently being necessary. Alternatives to hazardous cleaning chemicals will also be discussed in this paper.
Summary: Cleaning of pre and post heat treated parts is very important, because of the surface contaminants that can greatly influence the quality of the parts. This paper discusses various existing cleaning methods and their alternatives pertaining to heat treatment industries.

The Analysis Of Gas Flow In The Wind Tunnel Of High Pressure Gas Quenching Furnace

Authors

Y. Rong, Worcester Polytechnic Institute, Worcester, MA
J. Kang, Y. Luo, B. Liu, Tsinghua University, Beijing, China

Abstract

The structure of wind tunnel and nozzle system in gas quenching furnace determines the gas speed at the nozzles, which exerts considerable effect on the cooling rate and temperature distribution of the load. The gas flow in the wind tunnel was simulated by the software FLUENT. And the effects of various structural parameters, such as the chamfer of caecum of wind tunnel, the distance between the last nozzle and the caecum, the length and the tapering of the nozzle, on the gas velocity at the outlet of nozzles were investigated. The results show that the uniform of gas velocity at the outlet nozzles improves with the increase of the chamfer radius between the nozzle and wind tunnel and the use of tapered nozzle greatly improves the outflow gas velocity and its uniformity of distribution.
Summary: The gas flow in the wind tunnelgas quenching furnace was simulated by the software FLUENT. And the effects of various structural parameters , such as the chamfer of caecum of wind tunnel, the distance between the last nozzle and the caecum, the length and the tapering of the nozzle, on the gas velocity at the outlet of nozzles were investigated.

Effects of T6 Heat Treatment with Residual Heat of Casting on Microstructure and Mechanical Properties of 319 Aluminium Alloy Castings

Authors

Y. Rong, Worcester Polytechnic Institute, Worcester, MA
L. He, J. Kang, T. Huang, Tsinghua University, Beijing, China

Abstract

Among cast aluminium alloys, 319 ranks as one of the commercially important alloys used in automotive applications, on account of its excellent casting characteristics and good mechanical properties. It is necessary for 319 aluminium alloy castings to be heat treated (in T6 condition) for the improvement of their mechanical properties. However, heat treatment needs not only cycle time but also energy cost. The heat treatment with residual heat of aluminum castings, immediately after their solidification, can reduce reheating, cycle time and energy consumption. In this study, step-shape castings were heat treated in T6 and the new integrated technique, and the microstructural evolution was followed by optical and scanning electron microscopy. After aging, test bars were prepared for tensile strength and hardness tesing at room temperature, to study the effect of heat treatment on the mechanical properties. The results showed that the similar microstructures can be obtained by both the new technique and the traditional technique, in which dispersed and thinner Si particles can be observed and Cu can be dissolved effectively. The tensile strength was increased by about 10%-15% and the hardness was also improved by the integrated technique. Compared to traditional T6 technique, about 50% of solution time can be saved at most to acquire the equal tensile strength.
Summary: Generally, it is necessary for 319 aluminium alloy castings to be heat treated (T6 condition) for the improvement of their mechanical properties. However, heat treatment needs not only cycle time but also energy cost. The heat treatment with residual heat of aluminum castings, immediately after their solidification, can reduce reheating, cycle time and energy consumption. The Consolidated Engineering Company has developed the "Sand Lion 3-in-1" system, in which decoring and removal of the sand from the casting, sand reclamation and solution heat treatment of the casting can be performed at the same time. The research on this integrated technology of foundry and heat treatment is carried out to understand the microstructure evolution and mechanical properties of the castings. The effects of the heat treatment technology with residual heat of castings on the microstructure evolution of 319 aluminium alloy castings were experimentally investigated by using the methods of microscopic analysis, SEM and EDS. The results show that the shorter solution treatment time is needed to obtain the required mechanical properties and the coarsening of Si particles is restrained by the new technique. The effects of the new heat treatment technique on the thickness of castings were studied and the results show that there is almost no difference for the solutinized Cu content when the castings were solution treated for more than 3 hours, although there is big difference during the casting and the begining of solution treatment process. The effects of solution treatment time in the new technique on the mechanical properties were investigated. The test bars , which were solution treated, quenched and artificial aged, were tested and the results showed that the tensile strength and hardness of castings are increased by about 15% and 10% respectively. Compared to traditional T6 technique, about 50% of solution time can be saved at most to acquire the equal tensile strength. The shakeout and reclamation of the sand molds and cores was investigated and the results showed that they can be easily broken up and effectively reclaimed in the solution procedure of the new integrated technique. The effects of T6 heat treatment with residual heat of casting on microstructure and mechnical properties in 319 aluminium alloy were studied in the paper and the reasons of the improvement on the mechanical properties were given. The results can help to ditermine the process parameters and improve the production efficiency.

Numerical Simulation of High Pressure Gas Quenching Process of Workpieces

Authors

Y. Rong, Worcester Polytechnic Institute, Worcester, MA
J. Kang, Y. Luo, B. Liu, Tsinghua University, Beijing, China

Abstract

High pressure gas quenching process is simulated by computational fluid dynamics (CFD) method. A transient three-dimensional model of high-pressure gas quenching furnace is established on the FLUENT platform to simulate the gas flow in the furnace and cooling of the workpieces. Cooling curves of workpieces at different locations of the furnace are predicted. The simulation results are compared with the experimental ones. The effect of various parameters such as gas pressure, velocity, gas type and gas inlet temperature, on workpieces' cooling rate was quantitatively studied.
Summary: A transient three-dimensional model of high-pressure gas quenching furnace is established on the FLUENT platform to simulate the flow field in the furnace and temperature field of the workpieces. Cooling curves of workpieces at different locations of the furnace are predicted. The simulation results are compared with the experimental ones. The effect of different kinds of parameters on workpieces' cooling rate was quantitatively studied.

Electronic Substrate Materials Surface Texture Analysis for the Characterization of Rado-Wave Attenuation

Authors

Tracey Vincent

Abstract

Conductor loss is caused by power dissipation due to imperfect electrical conductivity and propagation. The theory that the overall attenuated loss primarily depends on the electrical path length has been investigated. It is well known that as electrical frequency increases, the signal will channel closer to the surface of the dielectric material; this phenomena is known as skin depth. The hypothesis is that the electrical path is a function of frequency, conductivity and surface roughness. Comparisons between measured conductor loss, the main component of attenuated loss at GHz frequencies, and conductor loss caused by path length of surface profile using length-scale fractal analysis, is investigated. The measured length of profile on rough surfaces is not unique, but depends on the scale of observation. Measurement of several AlN samples of different surface textures pertaining to different surface finishing processes is given. The total losses of all the samples have been measured; these losses have been broken into attenuated loss and reflected loss. Length-scale fractal results have been reviewed and correlation of length-scale results to conductor loss at multiple frequencies up to 25 GHz is discussed.

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