mary wells | University of Waterloo (original) (raw)

Papers by mary wells

Sensors, Sampling, and Simulation for Process Control

The Direct-Chill (DC) casting process is used in the non-ferrous metals industry to produce ingot... more The Direct-Chill (DC) casting process is used in the non-ferrous metals industry to produce ingots, blooms and cylindrical billets. During DC casting, primary cooling in the mould is followed by secondary cooling, in which the cast product surface is directly cooled by water jets. The formation of defects during the direct-chill casting process can be reduced by controlling the heat extraction in the secondary cooling zone during the start-up phase. The control and optimization of this process requires an accurate knowledge of the boundary conditions and their relationship with casting parameters. This research project studied the effect of different parameters on the heat transfer in the secondary cooling zone of the direct-chill casting process. This process was simulated by quenching instrumented samples of industrial DC-cast aluminum AA5 182 and magnesium AZ3 1 with water jets and recording the thermal history within the sample using sub-surface thermocouples. An inverse heat co...

Metals, 2021

A closed die forging process was developed to successfully forge an automotive suspension compone... more A closed die forging process was developed to successfully forge an automotive suspension component from AZ80 Mg at a variety of different forging temperatures (300 °C, 450 °C). The properties of the forged component were compared and contrasted with other research works on forged AZ80 Mg at both an intermediate forging and full-scale component forging level. The monotonic response, as well as the stress and strain-controlled fatigue behaviours, were characterized for the forged materials. Stress, strain and energy-based fatigue data were used as a basis for comparison of the durability performance. The effects of the starting material, forging temperature, forging geometry/configuration were all studied and aided in developing a deeper understanding of the process-structure-properties relationship. In general, there is a larger improvement in the material properties due to forging with cast base material as the microstructural modification which enhances both the strength and ducti...

Frattura ed Integrità Strutturale, 2020

The microstructural origins of premature fatigue failures were investigated on a variety of forge... more The microstructural origins of premature fatigue failures were investigated on a variety of forged components manufactured from AZ80 and ZK60 magnesium, both at the test specimen level and the full-scale component level. Both stress and strain-controlled approaches were used to characterize the macroscopically defect-free forged material behaviour as well as with varying levels of defect intensities. The effect of thermomechanical processing defects due to forging of a industrially relevant full-scale component were characterized and quantified using a variety of techniques. The fracture initiation and early crack growth behaviour was deterministically traced back to a combination of various effects having both geometric and microstructural origins, including poor fusion during forging, entrainment of contaminants sub-surface, as well as other inhomogeneities in the thermomechanical processing history. At the test specimen level, the fracture behaviour under both stress ...

Procedia Structural Integrity, 2020

The effect of the multiaxiality and proportionality of loading on the cyclic behaviour and early ... more The effect of the multiaxiality and proportionality of loading on the cyclic behaviour and early cracking behaviour was studied for closed die forged AZ80 Mg alloy. Several different loading paths were presented, uniaxial and biaxial with varying levels of nonproportionality. In multiaxial loading the effect of proportionality is only present on the shear response of the material and increasing levels of non-proportionality is detrimental to the fatigue life. When compared with proportional loading, a 50% reduction in life was observed under 90° out of phase non-proportional loading. The pure axial cracking behaviour is dominated by transverse cracks along the plane of maximum normal stress, whereas in pure shear the material exhibited longitudinal cracking (shear dominated) behaviour in LCF regime and helical cracking (normal stress dominated) in the HCF regime. The synergistic effects of each individual uniaxial cracking modes contribution towards the combined macroscopic cracking behaviour in multiaxial loading was investigated, and was dominated by transverse cracking when the shear strain energy density (SED) contribution to the total SED was low, and mixed cracking when the shear SED contribution was high.

Frattura ed Integrità Strutturale, 2020

Axial monotonic and load-controlled fatigue tests were performed to investigate the influence of ... more Axial monotonic and load-controlled fatigue tests were performed to investigate the influence of forging at various temperatures and different deformation rates, on both the microstructural and mechanical behaviour of extruded AZ31B magnesium alloy. The obtained microstructural analysis showed that the extruded AZ31B magnesium alloy possesses a bimodal grain structure with strong basal texture. In contrast, once forged, the material showed refined grains and a modified texture. A monotonic yield and ultimate tensile strength of about 223 MPa and 278 MPa were observed for the forged samples showing an increase of 18%, from the as-extruded material. The optimum forging condition was determined to be the coldest of the investigated temperatures, based on the improvement in both monotonic and cyclic properties vs. the as-extruded material. The fractographic analysis of the failure surfaces showed that ductile type fractures occurred in both asextruded and forged samples. However, more dimples and plastic deformation were identified in the fracture surfaces of the forged specimens. A significant improvement of fatigue life was also observed for all of the forged samples, in particular those forged at 400°C and 39 mm/min. Forging improved the fatigue life via a combination of grain refinement and texture modification resulting in improved strength and ductility.

Materials Science and Engineering: A, 2018

Hot deformation of a cast-homogenized ZK60 alloy was studied by compression at a temperature of 4... more Hot deformation of a cast-homogenized ZK60 alloy was studied by compression at a temperature of 450°C and a strain rate of 0.001s-1 to investigate microstructural evolution. The deformed microstructure was characterized using electron backscatter diffraction (EBSD) and high resolution transmission electron microscopy (HRTEM). EBSD observations of the deformed microstructure showed that hot deformation of this alloy resulted in a bimodal grain microstructure consisting of large pancaked unrecrystallized dendrites surrounded by recrystallized equiaxed fine grains. HRTEM studies revealed the presence of nano-(Zn-Zr)precipitates in the deformed microstructure. Due to the coherency of precipitates/matrix, the dislocations were pinned by the nano-precipitates inside the unrecrystallized grains and the dislocation motion inside the grains was impeded, hence, a substructure evolved. Consequently, dynamic recrystallization (DRX) was suppressed and deformation was concentrated inside the DRXed region.

Frattura ed Integrità Strutturale, 2016

Tensile and stress controlled fatigue tests were performed to investigate the influence of forgin... more Tensile and stress controlled fatigue tests were performed to investigate the influence of forging at a temperature of 400°C at different rates, on the performance of extruded AZ31B magnesium alloy. The obtained microstructural analysis showed that the extruded AZ31B magnesium alloy possesses a bimodal grain structure with strong basal texture. In contrast, the forged samples showed refined grains and a weaker texture. During tensile testing, a maximum yield and ultimate tensile strength of about 163 MPa and 268 MPa were obtained for the forged samples showing an increase of 102% and 7%, respectively from the as-extruded material. At the same time, a significant improvement of fatigue life was also observed for the sample forged at the rate of 100 mm/min. The fractographic analysis of the fracture surfaces showed that ductile type fractures occurred in both as-extruded and forged samples. However, more dimples and plastic deformation were identified in the fracture surfaces of the forged specimens. It is believed that forging improved the fatigue life by a combination of grain refinement and texture modification resulting in improved yield and ductility.

Vacuum, 2018

The hot flow stress behavior of three Al-Mg-Si alloys was determined by performing hot deformatio... more The hot flow stress behavior of three Al-Mg-Si alloys was determined by performing hot deformation compression tests on a Gleeble 3500 thermomechanical simulator over the temperature range 400 o C to 550 o C and at strain rates from 0.01 s-1 to 10 s-1. Using the hyperbolic sine constitutive model, constitutive parameters for prediction of the hot flow stress behavior of these different alloys were determined. The effect of chromium (Cr) addition and increased Mg-Si content on the average steady flow stress, constitutive and strain rate sensitivity (m) parameters was determined. For deformation at low strain rates (0.01-1 s-1), the alloy containing 0.2 wt % Cr exhibited higher average steady flow stress than the alloy with similar Mg-Si content and no Cr addition. The addition of 0.2 wt % Cr and an increase in Mg-Si content were observed to result in a decrease of the strain rate sensitivity parameter (m) and an increase in the activation energy for hot deformation. The predictive accuracy of the developed models was demonstrated by comparing the predicted and experimental flow stress behavior of alloy 3 at deformation conditions different from the temperature and strain rate conditions used to develop the models parameters. Results indicate that the developed model can accurately predict the alloy behavior at strain rate and temperature conditions beyond the range of model development.

Journal of Materials Processing Technology, 2018

This work examines the necessary process parameters for die quenching (DQ) during hot stamping an... more This work examines the necessary process parameters for die quenching (DQ) during hot stamping and subsequent age hardening and paint bake cycle (PBC) response for two alloys: AA7075 and a developmental 7xxx alloy (referred to as AA7xxx), with a lower Chromium content, higher Zirconium content and higher Zinc-to-Magnesium ratio in comparison to AA7075. For both alloys, a minimum solutionizing time of 8 minutes was found to be required, along with a minimum quench rate of 56°C/s and 27°C/s for AA7075 and AA7xxx, respectively. Two-step aging treatments, leveraging a paint bake cycle (PBC) of 177°C for 30 minutes as the second step, were considered after die quenching and were devised to achieve T6-or T76-level strengths. For AA7075, an aging treatment of 120°C for 8 hours, followed by the paint bake cycle (PBC) produced strength levels similar to a T6 temper. DSC experiments showed that the microstructure from this heat treatment was similar to a peak-aged T6 temper. For AA7xxx, a treatment of 100°C for 4 hours and followed by the paint bake produced a strength similar to a T76 temper, while 120°C for 3 hours followed by the paint bake yielded T6 strength levels. The properties of the custom aging treatments were validated through tensile tests. The resulting stress-strain curves show that it is possible to achieve T6 or T76 properties using a custom aging treatment incorporating the PBC that is 65-83% shorter than standard T6 or T76 treatments.

International Journal of Fatigue, 2018

Stress-controlled uniaxial "push-pull" fatigue testing was conducted on as-received (cast and ext... more Stress-controlled uniaxial "push-pull" fatigue testing was conducted on as-received (cast and extruded) and closed-die cast-forged and extruded-forged AZ80 Mg alloy. The as-cast material possessed random texture and somewhat symmetric cyclic responses. The extruded and forged materials possessed sharp basal texture and asymmetric cyclic responses. All materials exhibited tension/compression asymmetry in their cyclic response to varying degrees, depending on the thermomechanical processing conditions. It was discovered that the style of closed-die forging being investigated had spatially varying properties with texture orientations which varied based on the local forging directions and intensities which were dependent on the starting texture as well as the thermomechanical history. Under fatigue testing, the materials all developed some form of mean strain, with the nature and magnitude of this mean strain being dependent on primarily its texture intensity and propensity to twin in either tension or compression reversals. The type of mean strain (tensile or compressive) depends upon both the orientation and intensity of the starting texture of material. The texture induced ratcheting and resulting mean strain evolution was most pronounced in the as-cast material and had a significant impact on the fatigue life. Following forging, the material exhibited an increase in fatigue life of anywhere from 2 to 15 times for the cast then forged material and more modest yet still significant 8 times longer at stress amplitudes around 140 MPa for the extruded then forged material. The extruded forged material exhibited similar fatigue lives to that of the base material at stress amplitudes which approached the yield strength. The nature of the mean stress development and degree of fatigue life improvement depended on the processing conditions and the type of base material (cast or extruded) utilized to create the forging. Two energy based models were utilized to predict the life of the forged material, and gave a reliable life prediction for a variety of material conditions that were investigated.

steel research international, 2008

Using a unique pilot facility a series of tests were conducted using three top jets to simulate t... more Using a unique pilot facility a series of tests were conducted using three top jets to simulate the heat transfer that occurs during run‐out table (ROT) cooling. Steel samples instrumented with internal thermocouples were tested on this facility and the effect of top jet configuration (nozzle spacing of 40 to 115mm), and water flow rate (15 and 30 1/min) were quantified using moving plate samples. The multiple top jet work indicated that heat transfer across the plate width varies significantly and is high directly under the nozzle but decreases rapidly away from the nozzle in the interaction region. As cooling progresses a much larger wetted region occurs and more uniform cooling is experienced across the plate. Multiple jet cooling experiments have also confirmed that nozzle spacing does have an effect on heat transfer. This effect is predominate in the interaction region where closer nozzle spacing leads to enhanced and more uniform heat transfer in the lateral direction across t...

International Journal of Fatigue, 2017

Tensile and strain-controlled fatigue tests were performed to investigate the influence of forgin... more Tensile and strain-controlled fatigue tests were performed to investigate the influence of forging on the performance of cast AZ80 magnesium alloy. The obtained microstructural analysis showed that the as-cast AZ80 magnesium alloy has dendritic α-Mg phase with eutectic Mg 17 Al 12 morphology and a random texture. In contrast, the forged samples showed refined grains and a strong basal texture. During tensile testing, a maximum yield and ultimate tensile strength of 182 MPa and 312 MPa were obtained for the forged samples, representing increases of 121% and 33%, respectively, from the as-cast condition. At the same time, a significant improvement (73%) in ductility was obtained in forged samples. It was also observed that the forged samples achieved comparatively longer fatigue life under strain-controlled cyclic loading. Analysis of the fracture surfaces showed that a cleavage-type morphology was typical for the ascast samples, while the occurrence of dimples and other evidence of plastic deformation were identified in the fracture surfaces of the forged specimens, indicating a more ductile response. Forging caused grain refinement and texture modification, both of which enhance alloy performance by improving strength and ductility, and leading to longer fatigue life. Strain and energy-based models were investigated for their suitability to predict the life of the forged material. Both the Smith-Watson Topper and the Jahed-Varvani energy-based models gave reliable life prediction.

Krane/Proceedings, 2013

Novelis Inc. recently developed and patented a unique Direct Chill (DC) casting process whereby t... more Novelis Inc. recently developed and patented a unique Direct Chill (DC) casting process whereby two different alloys can be cast simultaneously, producing a laminated aluminum ingot, known as Fusion™ 1 casting. In this process, a high quality metallurgical bond is formed between the two simultaneously cast alloys; the mechanism of how this bond formation occurs between the two alloys is not clearly understood. Since direct observation of wetting and interface formation in the Fusion casting process is difficult to obtain in practice, due to temperature and proximity issues, an analog test was designed to mimic the processes on the laboratory scale. The apparatus provides a means of controlling the basic variables thought to influence bond formation in Fusion casting, namely: i) the relative temperatures of the two alloys in contact, ii) the sample contact time, and iii) surface oxidation. The results of two test series will be presented, highlighting the relative importance these variables have on as-cast interface quality.

Materials Science and Technology, 2004

In the metal casting industry, an improvement of component quality depends mainly on better contr... more In the metal casting industry, an improvement of component quality depends mainly on better control over the production parameters. Thus, computer-aided cooling curve thermal analysis is a very useful method for easy and fast evaluation of a variety of properties. In this work, the effect of different cooling rates (1.2-7.2°C s-1) on solidification parameters and dendrite coherency point (DCP) of ADC12 aluminum alloy was investigated by thermal analysis. The results revealed that solidification parameters and dendrite coherency point are influenced by variation of cooling rate. Increasing the cooling rate can increase the temperature interval of coherency (T N-T DCP) and coherency fraction solid (f DCP s) about 31°C and 11 %, respectively, but the coherency time (t DCP) decreases from 130 to 33 s. Therefore, increasing the cooling rate postpones the dendrite coherency, and the dendrites become coherent later. Keywords ADC12 aluminum alloy Á Thermal analysis Á Cooling rate Á Dendrite coherency point (DCP) Á Solidification

Journal of Magnesium and Alloys, 2013

The effect of setback distance on the thermo-mechanical behavior of the strip during twin roll ca... more The effect of setback distance on the thermo-mechanical behavior of the strip during twin roll casting (TRC) of an AZ31 magnesium alloy was modeled using finite element method (FEM). Model validation was done by comparing the predicted and measured exit strip surface temperature as well as the secondary dendrite arm spacing (SDAS) through the thickness of the sheet to those measured during experiments. Model results showed as the setback distance increases, the strip exit temperature decreases and the solidification front moves toward the entry of the roll gap. The cast strip also experiences more plastic deformation and consequently, the normal stress on the strip surface and effective strain at the strip center-line increase. Moreover, higher separating forces were predicted for longer setback distances. Model predictions showed that changing the setback distance by varying the final thickness has a more significant effect on the temperature and stress-strain fields than altering the nozzle opening height.

Magnesium Technology 2012, 2012

A 2-D coupled thermal-fluid-stress model was developed and used to simulate the twin roll casting... more A 2-D coupled thermal-fluid-stress model was developed and used to simulate the twin roll casting (TRC) of an AZ31 magnesium alloy using the commercial software package, ALSIM. The model was used to predict the fluid flow, temperature distribution and mechanical behavior of AZ31 magnesium alloy in the roll bite. An important parameter in controlling the TRC process is the set-back distance; the distance between the nozzle entry to the kissing point of the rolls. There are two approaches to increase the set-back: 1) increasing the entry thickness and 2) decreasing the final strip thickness. In this study the effect of set-back distance and casting speed on the thermo-mechanical behavior of the strip during TRC has been studied. The thermo-mechanical behavior of the strip has a significant effect on the final quality as defect formation depends on such behavior.

The annealing behaviour of commercial precipitation hardened alloys is complex as it may involve ... more The annealing behaviour of commercial precipitation hardened alloys is complex as it may involve the simultaneous occurrence of recovery, recrystallization and precipitation. The present work examines the effect of different initial precipitation states on the recrystallization behaviour of a cold rolled aluminum alloy, AA6111. It is found that the recrystallization kinetics are extremely sluggish irrespective of the starting precipitation state. Re-precipitation of Q phase during annealing is found to occur primarily along grain boundaries and on shear bands. Recrystallized grain size is controlled by the spacing of precipitates in the structure. Larger precipitate spacing allows recrystallized grains to grow coarser resulting in a wider distribution of recrystallized grain size.

Metallurgical and Materials Transactions B, 2004

Sensors, Sampling, and Simulation for Process Control

The Direct-Chill (DC) casting process is used in the non-ferrous metals industry to produce ingot... more The Direct-Chill (DC) casting process is used in the non-ferrous metals industry to produce ingots, blooms and cylindrical billets. During DC casting, primary cooling in the mould is followed by secondary cooling, in which the cast product surface is directly cooled by water jets. The formation of defects during the direct-chill casting process can be reduced by controlling the heat extraction in the secondary cooling zone during the start-up phase. The control and optimization of this process requires an accurate knowledge of the boundary conditions and their relationship with casting parameters. This research project studied the effect of different parameters on the heat transfer in the secondary cooling zone of the direct-chill casting process. This process was simulated by quenching instrumented samples of industrial DC-cast aluminum AA5 182 and magnesium AZ3 1 with water jets and recording the thermal history within the sample using sub-surface thermocouples. An inverse heat co...

Metals, 2021

A closed die forging process was developed to successfully forge an automotive suspension compone... more A closed die forging process was developed to successfully forge an automotive suspension component from AZ80 Mg at a variety of different forging temperatures (300 °C, 450 °C). The properties of the forged component were compared and contrasted with other research works on forged AZ80 Mg at both an intermediate forging and full-scale component forging level. The monotonic response, as well as the stress and strain-controlled fatigue behaviours, were characterized for the forged materials. Stress, strain and energy-based fatigue data were used as a basis for comparison of the durability performance. The effects of the starting material, forging temperature, forging geometry/configuration were all studied and aided in developing a deeper understanding of the process-structure-properties relationship. In general, there is a larger improvement in the material properties due to forging with cast base material as the microstructural modification which enhances both the strength and ducti...

Frattura ed Integrità Strutturale, 2020

The microstructural origins of premature fatigue failures were investigated on a variety of forge... more The microstructural origins of premature fatigue failures were investigated on a variety of forged components manufactured from AZ80 and ZK60 magnesium, both at the test specimen level and the full-scale component level. Both stress and strain-controlled approaches were used to characterize the macroscopically defect-free forged material behaviour as well as with varying levels of defect intensities. The effect of thermomechanical processing defects due to forging of a industrially relevant full-scale component were characterized and quantified using a variety of techniques. The fracture initiation and early crack growth behaviour was deterministically traced back to a combination of various effects having both geometric and microstructural origins, including poor fusion during forging, entrainment of contaminants sub-surface, as well as other inhomogeneities in the thermomechanical processing history. At the test specimen level, the fracture behaviour under both stress ...

Procedia Structural Integrity, 2020

The effect of the multiaxiality and proportionality of loading on the cyclic behaviour and early ... more The effect of the multiaxiality and proportionality of loading on the cyclic behaviour and early cracking behaviour was studied for closed die forged AZ80 Mg alloy. Several different loading paths were presented, uniaxial and biaxial with varying levels of nonproportionality. In multiaxial loading the effect of proportionality is only present on the shear response of the material and increasing levels of non-proportionality is detrimental to the fatigue life. When compared with proportional loading, a 50% reduction in life was observed under 90° out of phase non-proportional loading. The pure axial cracking behaviour is dominated by transverse cracks along the plane of maximum normal stress, whereas in pure shear the material exhibited longitudinal cracking (shear dominated) behaviour in LCF regime and helical cracking (normal stress dominated) in the HCF regime. The synergistic effects of each individual uniaxial cracking modes contribution towards the combined macroscopic cracking behaviour in multiaxial loading was investigated, and was dominated by transverse cracking when the shear strain energy density (SED) contribution to the total SED was low, and mixed cracking when the shear SED contribution was high.

Frattura ed Integrità Strutturale, 2020

Axial monotonic and load-controlled fatigue tests were performed to investigate the influence of ... more Axial monotonic and load-controlled fatigue tests were performed to investigate the influence of forging at various temperatures and different deformation rates, on both the microstructural and mechanical behaviour of extruded AZ31B magnesium alloy. The obtained microstructural analysis showed that the extruded AZ31B magnesium alloy possesses a bimodal grain structure with strong basal texture. In contrast, once forged, the material showed refined grains and a modified texture. A monotonic yield and ultimate tensile strength of about 223 MPa and 278 MPa were observed for the forged samples showing an increase of 18%, from the as-extruded material. The optimum forging condition was determined to be the coldest of the investigated temperatures, based on the improvement in both monotonic and cyclic properties vs. the as-extruded material. The fractographic analysis of the failure surfaces showed that ductile type fractures occurred in both asextruded and forged samples. However, more dimples and plastic deformation were identified in the fracture surfaces of the forged specimens. A significant improvement of fatigue life was also observed for all of the forged samples, in particular those forged at 400°C and 39 mm/min. Forging improved the fatigue life via a combination of grain refinement and texture modification resulting in improved strength and ductility.

Materials Science and Engineering: A, 2018

Hot deformation of a cast-homogenized ZK60 alloy was studied by compression at a temperature of 4... more Hot deformation of a cast-homogenized ZK60 alloy was studied by compression at a temperature of 450°C and a strain rate of 0.001s-1 to investigate microstructural evolution. The deformed microstructure was characterized using electron backscatter diffraction (EBSD) and high resolution transmission electron microscopy (HRTEM). EBSD observations of the deformed microstructure showed that hot deformation of this alloy resulted in a bimodal grain microstructure consisting of large pancaked unrecrystallized dendrites surrounded by recrystallized equiaxed fine grains. HRTEM studies revealed the presence of nano-(Zn-Zr)precipitates in the deformed microstructure. Due to the coherency of precipitates/matrix, the dislocations were pinned by the nano-precipitates inside the unrecrystallized grains and the dislocation motion inside the grains was impeded, hence, a substructure evolved. Consequently, dynamic recrystallization (DRX) was suppressed and deformation was concentrated inside the DRXed region.

Frattura ed Integrità Strutturale, 2016

Tensile and stress controlled fatigue tests were performed to investigate the influence of forgin... more Tensile and stress controlled fatigue tests were performed to investigate the influence of forging at a temperature of 400°C at different rates, on the performance of extruded AZ31B magnesium alloy. The obtained microstructural analysis showed that the extruded AZ31B magnesium alloy possesses a bimodal grain structure with strong basal texture. In contrast, the forged samples showed refined grains and a weaker texture. During tensile testing, a maximum yield and ultimate tensile strength of about 163 MPa and 268 MPa were obtained for the forged samples showing an increase of 102% and 7%, respectively from the as-extruded material. At the same time, a significant improvement of fatigue life was also observed for the sample forged at the rate of 100 mm/min. The fractographic analysis of the fracture surfaces showed that ductile type fractures occurred in both as-extruded and forged samples. However, more dimples and plastic deformation were identified in the fracture surfaces of the forged specimens. It is believed that forging improved the fatigue life by a combination of grain refinement and texture modification resulting in improved yield and ductility.

Vacuum, 2018

The hot flow stress behavior of three Al-Mg-Si alloys was determined by performing hot deformatio... more The hot flow stress behavior of three Al-Mg-Si alloys was determined by performing hot deformation compression tests on a Gleeble 3500 thermomechanical simulator over the temperature range 400 o C to 550 o C and at strain rates from 0.01 s-1 to 10 s-1. Using the hyperbolic sine constitutive model, constitutive parameters for prediction of the hot flow stress behavior of these different alloys were determined. The effect of chromium (Cr) addition and increased Mg-Si content on the average steady flow stress, constitutive and strain rate sensitivity (m) parameters was determined. For deformation at low strain rates (0.01-1 s-1), the alloy containing 0.2 wt % Cr exhibited higher average steady flow stress than the alloy with similar Mg-Si content and no Cr addition. The addition of 0.2 wt % Cr and an increase in Mg-Si content were observed to result in a decrease of the strain rate sensitivity parameter (m) and an increase in the activation energy for hot deformation. The predictive accuracy of the developed models was demonstrated by comparing the predicted and experimental flow stress behavior of alloy 3 at deformation conditions different from the temperature and strain rate conditions used to develop the models parameters. Results indicate that the developed model can accurately predict the alloy behavior at strain rate and temperature conditions beyond the range of model development.

Journal of Materials Processing Technology, 2018

This work examines the necessary process parameters for die quenching (DQ) during hot stamping an... more This work examines the necessary process parameters for die quenching (DQ) during hot stamping and subsequent age hardening and paint bake cycle (PBC) response for two alloys: AA7075 and a developmental 7xxx alloy (referred to as AA7xxx), with a lower Chromium content, higher Zirconium content and higher Zinc-to-Magnesium ratio in comparison to AA7075. For both alloys, a minimum solutionizing time of 8 minutes was found to be required, along with a minimum quench rate of 56°C/s and 27°C/s for AA7075 and AA7xxx, respectively. Two-step aging treatments, leveraging a paint bake cycle (PBC) of 177°C for 30 minutes as the second step, were considered after die quenching and were devised to achieve T6-or T76-level strengths. For AA7075, an aging treatment of 120°C for 8 hours, followed by the paint bake cycle (PBC) produced strength levels similar to a T6 temper. DSC experiments showed that the microstructure from this heat treatment was similar to a peak-aged T6 temper. For AA7xxx, a treatment of 100°C for 4 hours and followed by the paint bake produced a strength similar to a T76 temper, while 120°C for 3 hours followed by the paint bake yielded T6 strength levels. The properties of the custom aging treatments were validated through tensile tests. The resulting stress-strain curves show that it is possible to achieve T6 or T76 properties using a custom aging treatment incorporating the PBC that is 65-83% shorter than standard T6 or T76 treatments.

International Journal of Fatigue, 2018

Stress-controlled uniaxial "push-pull" fatigue testing was conducted on as-received (cast and ext... more Stress-controlled uniaxial "push-pull" fatigue testing was conducted on as-received (cast and extruded) and closed-die cast-forged and extruded-forged AZ80 Mg alloy. The as-cast material possessed random texture and somewhat symmetric cyclic responses. The extruded and forged materials possessed sharp basal texture and asymmetric cyclic responses. All materials exhibited tension/compression asymmetry in their cyclic response to varying degrees, depending on the thermomechanical processing conditions. It was discovered that the style of closed-die forging being investigated had spatially varying properties with texture orientations which varied based on the local forging directions and intensities which were dependent on the starting texture as well as the thermomechanical history. Under fatigue testing, the materials all developed some form of mean strain, with the nature and magnitude of this mean strain being dependent on primarily its texture intensity and propensity to twin in either tension or compression reversals. The type of mean strain (tensile or compressive) depends upon both the orientation and intensity of the starting texture of material. The texture induced ratcheting and resulting mean strain evolution was most pronounced in the as-cast material and had a significant impact on the fatigue life. Following forging, the material exhibited an increase in fatigue life of anywhere from 2 to 15 times for the cast then forged material and more modest yet still significant 8 times longer at stress amplitudes around 140 MPa for the extruded then forged material. The extruded forged material exhibited similar fatigue lives to that of the base material at stress amplitudes which approached the yield strength. The nature of the mean stress development and degree of fatigue life improvement depended on the processing conditions and the type of base material (cast or extruded) utilized to create the forging. Two energy based models were utilized to predict the life of the forged material, and gave a reliable life prediction for a variety of material conditions that were investigated.

steel research international, 2008

Using a unique pilot facility a series of tests were conducted using three top jets to simulate t... more Using a unique pilot facility a series of tests were conducted using three top jets to simulate the heat transfer that occurs during run‐out table (ROT) cooling. Steel samples instrumented with internal thermocouples were tested on this facility and the effect of top jet configuration (nozzle spacing of 40 to 115mm), and water flow rate (15 and 30 1/min) were quantified using moving plate samples. The multiple top jet work indicated that heat transfer across the plate width varies significantly and is high directly under the nozzle but decreases rapidly away from the nozzle in the interaction region. As cooling progresses a much larger wetted region occurs and more uniform cooling is experienced across the plate. Multiple jet cooling experiments have also confirmed that nozzle spacing does have an effect on heat transfer. This effect is predominate in the interaction region where closer nozzle spacing leads to enhanced and more uniform heat transfer in the lateral direction across t...

International Journal of Fatigue, 2017

Tensile and strain-controlled fatigue tests were performed to investigate the influence of forgin... more Tensile and strain-controlled fatigue tests were performed to investigate the influence of forging on the performance of cast AZ80 magnesium alloy. The obtained microstructural analysis showed that the as-cast AZ80 magnesium alloy has dendritic α-Mg phase with eutectic Mg 17 Al 12 morphology and a random texture. In contrast, the forged samples showed refined grains and a strong basal texture. During tensile testing, a maximum yield and ultimate tensile strength of 182 MPa and 312 MPa were obtained for the forged samples, representing increases of 121% and 33%, respectively, from the as-cast condition. At the same time, a significant improvement (73%) in ductility was obtained in forged samples. It was also observed that the forged samples achieved comparatively longer fatigue life under strain-controlled cyclic loading. Analysis of the fracture surfaces showed that a cleavage-type morphology was typical for the ascast samples, while the occurrence of dimples and other evidence of plastic deformation were identified in the fracture surfaces of the forged specimens, indicating a more ductile response. Forging caused grain refinement and texture modification, both of which enhance alloy performance by improving strength and ductility, and leading to longer fatigue life. Strain and energy-based models were investigated for their suitability to predict the life of the forged material. Both the Smith-Watson Topper and the Jahed-Varvani energy-based models gave reliable life prediction.

Krane/Proceedings, 2013

Novelis Inc. recently developed and patented a unique Direct Chill (DC) casting process whereby t... more Novelis Inc. recently developed and patented a unique Direct Chill (DC) casting process whereby two different alloys can be cast simultaneously, producing a laminated aluminum ingot, known as Fusion™ 1 casting. In this process, a high quality metallurgical bond is formed between the two simultaneously cast alloys; the mechanism of how this bond formation occurs between the two alloys is not clearly understood. Since direct observation of wetting and interface formation in the Fusion casting process is difficult to obtain in practice, due to temperature and proximity issues, an analog test was designed to mimic the processes on the laboratory scale. The apparatus provides a means of controlling the basic variables thought to influence bond formation in Fusion casting, namely: i) the relative temperatures of the two alloys in contact, ii) the sample contact time, and iii) surface oxidation. The results of two test series will be presented, highlighting the relative importance these variables have on as-cast interface quality.

Materials Science and Technology, 2004

In the metal casting industry, an improvement of component quality depends mainly on better contr... more In the metal casting industry, an improvement of component quality depends mainly on better control over the production parameters. Thus, computer-aided cooling curve thermal analysis is a very useful method for easy and fast evaluation of a variety of properties. In this work, the effect of different cooling rates (1.2-7.2°C s-1) on solidification parameters and dendrite coherency point (DCP) of ADC12 aluminum alloy was investigated by thermal analysis. The results revealed that solidification parameters and dendrite coherency point are influenced by variation of cooling rate. Increasing the cooling rate can increase the temperature interval of coherency (T N-T DCP) and coherency fraction solid (f DCP s) about 31°C and 11 %, respectively, but the coherency time (t DCP) decreases from 130 to 33 s. Therefore, increasing the cooling rate postpones the dendrite coherency, and the dendrites become coherent later. Keywords ADC12 aluminum alloy Á Thermal analysis Á Cooling rate Á Dendrite coherency point (DCP) Á Solidification

Journal of Magnesium and Alloys, 2013

The effect of setback distance on the thermo-mechanical behavior of the strip during twin roll ca... more The effect of setback distance on the thermo-mechanical behavior of the strip during twin roll casting (TRC) of an AZ31 magnesium alloy was modeled using finite element method (FEM). Model validation was done by comparing the predicted and measured exit strip surface temperature as well as the secondary dendrite arm spacing (SDAS) through the thickness of the sheet to those measured during experiments. Model results showed as the setback distance increases, the strip exit temperature decreases and the solidification front moves toward the entry of the roll gap. The cast strip also experiences more plastic deformation and consequently, the normal stress on the strip surface and effective strain at the strip center-line increase. Moreover, higher separating forces were predicted for longer setback distances. Model predictions showed that changing the setback distance by varying the final thickness has a more significant effect on the temperature and stress-strain fields than altering the nozzle opening height.

Magnesium Technology 2012, 2012

A 2-D coupled thermal-fluid-stress model was developed and used to simulate the twin roll casting... more A 2-D coupled thermal-fluid-stress model was developed and used to simulate the twin roll casting (TRC) of an AZ31 magnesium alloy using the commercial software package, ALSIM. The model was used to predict the fluid flow, temperature distribution and mechanical behavior of AZ31 magnesium alloy in the roll bite. An important parameter in controlling the TRC process is the set-back distance; the distance between the nozzle entry to the kissing point of the rolls. There are two approaches to increase the set-back: 1) increasing the entry thickness and 2) decreasing the final strip thickness. In this study the effect of set-back distance and casting speed on the thermo-mechanical behavior of the strip during TRC has been studied. The thermo-mechanical behavior of the strip has a significant effect on the final quality as defect formation depends on such behavior.

The annealing behaviour of commercial precipitation hardened alloys is complex as it may involve ... more The annealing behaviour of commercial precipitation hardened alloys is complex as it may involve the simultaneous occurrence of recovery, recrystallization and precipitation. The present work examines the effect of different initial precipitation states on the recrystallization behaviour of a cold rolled aluminum alloy, AA6111. It is found that the recrystallization kinetics are extremely sluggish irrespective of the starting precipitation state. Re-precipitation of Q phase during annealing is found to occur primarily along grain boundaries and on shear bands. Recrystallized grain size is controlled by the spacing of precipitates in the structure. Larger precipitate spacing allows recrystallized grains to grow coarser resulting in a wider distribution of recrystallized grain size.

Metallurgical and Materials Transactions B, 2004