Title page for ETD etd-050106-174639

Document Type dissertation

Author Name Ma, Shuhui

URN etd-050106-174639

Title A Methodology to Predict the Effects of Quench Rates on Mechanical Properties of Cast Aluminum Alloys

Degree PhD

Department Materials Science & Engineering

Advisors
Richard D. Sisson, Jr., Advisor
Diran Apelian, Committee Member
Makhlouf M. Makhlouf, Committee Member
Yiming(Kevin) Rong, Committee Member
Scott MacKenzie, Committee Member

Keywords
Time-Temperature-Property curve
Jominy End Quench
ANOVA analysis. Quench Factor Analysis
Taguchi design
Polymer quench
Cast Al-Si-Mg alloys
Quenching
Heat treatment

Date of Presentation/Defense 2006-03-24

Availability unrestricted

Abstract
The physical properties of polymer quench bath directly affect the cooling rate of a quenched part. These properties include the type of quenchant, its temperature, concentration, and agitation level. These parameters must be controlled to optimize the quenching process in terms of alloy microstructure, properties and performance. Statistically designed experiments have been performed to investigate the effects of the process parameters (i.e. polymer concentration and agitation) on the heat transfer behavior of cast aluminum alloy A356 in aqueous solution of Aqua-Quench 260 using the CHTE quenching-agitation system. The experiments were designed using Taguchi technique and the experimental results were analyzed with Analysis of Variance (ANOVA) based on the average cooling rate. It is found that average cooling rate dramatically decreases with the increase in polymer concentration. Agitation only enhances the average cooling rate at low and medium concentration levels. From ANOVA analysis, the process parameter that affects the variation of average cooling rate most is the polymer concentration, its percentage contribution is 97%. The effects from agitation and the interaction between polymer concentration and tank agitation are insignificant.

The mechanical properties of age-hardenable Al-Si-Mg alloys depend on the rate at which the alloy is cooled after the solutionizing heat treatment. A model based on the transformation kinetics is needed for the design engineer to quantify the effects of quenching rates on the as-aged properties. Quench Factor analysis was developed by Staley to describe the relationship between the cooling rate and the mechanical properties of an age-hardenable alloy. This method has been previously used to successfully predict yield strength, hardness of wrought aluminum alloys. However, the Quench Factor data for aluminum castings are still rare in the literature. In this study, the Jominy End Quench method was used to experimentally collect the time-temperature and hardness data as the inputs for Quench Factor modeling. Multiple linear regression analysis was performed on the experimental data to estimate the kinetic parameters during quenching. Time-Temperature-Property curves of cast aluminum alloy A356 were generated using the estimated kinetic parameters. Experimental verification was performed on a L5 lost foam cast engine head. The predicted hardness agreed well with that experimentally measured.

Files
Ma.pdf

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Document Type	dissertation
Author Name	Ma, Shuhui
URN	etd-050106-174639
Title	A Methodology to Predict the Effects of Quench Rates on Mechanical Properties of Cast Aluminum Alloys
Degree	PhD
Department	Materials Science & Engineering
Advisors	Richard D. Sisson, Jr., Advisor Diran Apelian, Committee Member Makhlouf M. Makhlouf, Committee Member Yiming(Kevin) Rong, Committee Member Scott MacKenzie, Committee Member
Keywords	Time-Temperature-Property curve Jominy End Quench ANOVA analysis. Quench Factor Analysis Taguchi design Polymer quench Cast Al-Si-Mg alloys Quenching Heat treatment
Date of Presentation/Defense	2006-03-24
Availability	unrestricted
Abstract The physical properties of polymer quench bath directly affect the cooling rate of a quenched part. These properties include the type of quenchant, its temperature, concentration, and agitation level. These parameters must be controlled to optimize the quenching process in terms of alloy microstructure, properties and performance. Statistically designed experiments have been performed to investigate the effects of the process parameters (i.e. polymer concentration and agitation) on the heat transfer behavior of cast aluminum alloy A356 in aqueous solution of Aqua-Quench 260 using the CHTE quenching-agitation system. The experiments were designed using Taguchi technique and the experimental results were analyzed with Analysis of Variance (ANOVA) based on the average cooling rate. It is found that average cooling rate dramatically decreases with the increase in polymer concentration. Agitation only enhances the average cooling rate at low and medium concentration levels. From ANOVA analysis, the process parameter that affects the variation of average cooling rate most is the polymer concentration, its percentage contribution is 97%. The effects from agitation and the interaction between polymer concentration and tank agitation are insignificant. The mechanical properties of age-hardenable Al-Si-Mg alloys depend on the rate at which the alloy is cooled after the solutionizing heat treatment. A model based on the transformation kinetics is needed for the design engineer to quantify the effects of quenching rates on the as-aged properties. Quench Factor analysis was developed by Staley to describe the relationship between the cooling rate and the mechanical properties of an age-hardenable alloy. This method has been previously used to successfully predict yield strength, hardness of wrought aluminum alloys. However, the Quench Factor data for aluminum castings are still rare in the literature. In this study, the Jominy End Quench method was used to experimentally collect the time-temperature and hardness data as the inputs for Quench Factor modeling. Multiple linear regression analysis was performed on the experimental data to estimate the kinetic parameters during quenching. Time-Temperature-Property curves of cast aluminum alloy A356 were generated using the estimated kinetic parameters. Experimental verification was performed on a L5 lost foam cast engine head. The predicted hardness agreed well with that experimentally measured.
Files	Ma.pdf