title: The Effect of Grain Refinement on the Castability of Magnesium-Aluminium Alloys

authors: Loughnane, Timothy Kevin

subjects: Magnesium

abstract: Rapidly increasing fuel prices and global pressures to reduce the harmful effects of vehicle emissions are forcing vehicle manufacturers to look at alternative materials to reduce the mass of the vehicles they produce. This has led to an increase in the research and development of magnesium alloys for use in automotive applications, and the methods used to produce them. With a density two-thirds that of aluminium alloys, and one quarter that of steel, magnesium alloys are continually being investigated as possible replacements for the production of automotive castings such as wheels and engine blocks. However, there is presently a lack of understanding of the effects of common alloy additions that refine the as-cast microstructure on the castability of the casting alloys in question.

The most popular magnesium alloys for large automotive castings are based on the magnesium-aluminium alloy system. For the work presented in this thesis, two of the most common Mg-Al alloys, AZ91E and AM60B, were chosen to determine the effect of grain refinement on the castability of Mg-Al alloys. An experimental mould has been designed and developed to emulate the geometry, filling, and solidification of an alloy wheel casting. Two different grain refiners were investigated at varying addition levels to determine the effect of different levels of grain refinement on the castability of the two alloys. Castability, defined as the ability to produce sound castings from a particular alloy, has been assessed through visual examination of external casting defects, X-ray radiography of internal defects, as well as grain size and porosity level analysis of all samples produced.

It has been found that for both AZ91E and AM60B, an increase in the level of grain refinement achieved lead to an increase in the occurrence and severity of the surface slumping defect in the castings produced. Conversely, increased levels of grain refinement were found to reduce or totally eliminate the occurrence of the hot tearing defect in both alloys.

Contrary to popular belief, grain refinement was found to increase the level of internal shrinkage porosity in the Mg-Al castings. This was especially the case in the poorly fed regions of the casting, such as the junction between the spoke and rim sections. This is due to the increased reliance on interdendritic feeding of liquid to compensate for shrinkage during the latter stages of solidification in such areas, where solidification does not proceed directionally towards the feeding reservoirs. An increase in the level of grain refinement means the interdendritic network becomes heavily constricted, resulting in a rapid increase in the feeding pressure required to feed metal to the areas where it is required.

This study has also resulted in the development of a novel method of successfully and consistently introducing carbon to a Mg-Al alloy melt. This has in the past been identified as a major issue to overcome when adding carbon based grain refiners to Mg-Al alloy melts.

text: The Effect of Grain Refinement on the Castability of Magnesium-Aluminium Alloys Rapidly increasing fuel prices and global pressures to reduce the harmful effects of vehicle emissions are forcing vehicle manufacturers to look at alternative materials to reduce the mass of the vehicles they produce. This has led to an increase in the research and development of magnesium alloys for use in automotive applications, and the methods used to produce them. With a density two-thirds that of aluminium alloys, and one quarter that of steel, magnesium alloys are continually being investigated as possible replacements for the production of automotive castings such as wheels and engine blocks. However, there is presently a lack of understanding of the effects of common alloy additions that refine the as-cast microstructure on the castability of the casting alloys in question.

The most popular magnesium alloys for large automotive castings are based on the magnesium-aluminium alloy system. For the work presented in this thesis, two of the most common Mg-Al alloys, AZ91E and AM60B, were chosen to determine the effect of grain refinement on the castability of Mg-Al alloys. An experimental mould has been designed and developed to emulate the geometry, filling, and solidification of an alloy wheel casting. Two different grain refiners were investigated at varying addition levels to determine the effect of different levels of grain refinement on the castability of the two alloys. Castability, defined as the ability to produce sound castings from a particular alloy, has been assessed through visual examination of external casting defects, X-ray radiography of internal defects, as well as grain size and porosity level analysis of all samples produced.

It has been found that for both AZ91E and AM60B, an increase in the level of grain refinement achieved lead to an increase in the occurrence and severity of the surface slumping defect in the castings produced. Conversely, increased levels of grain refinement were found to reduce or totally eliminate the occurrence of the hot tearing defect in both alloys.

Contrary to popular belief, grain refinement was found to increase the level of internal shrinkage porosity in the Mg-Al castings. This was especially the case in the poorly fed regions of the casting, such as the junction between the spoke and rim sections. This is due to the increased reliance on interdendritic feeding of liquid to compensate for shrinkage during the latter stages of solidification in such areas, where solidification does not proceed directionally towards the feeding reservoirs. An increase in the level of grain refinement means the interdendritic network becomes heavily constricted, resulting in a rapid increase in the feeding pressure required to feed metal to the areas where it is required.

This study has also resulted in the development of a novel method of successfully and consistently introducing carbon to a Mg-Al alloy melt. This has in the past been identified as a major issue to overcome when adding carbon based grain refiners to Mg-Al alloy melts.

year: 2007

title: A Historical Analysis of the Status of Women in New Zealand: Has CEDAW had an Impact?

authors: Jones, Heidi

subjects: women

abstract: This thesis analyses the current and historical status of women in New Zealand for the purpose of discovering why full equality between men and women has not yet been achieved. This object will be accomplished by analysing, comparing and contrasting the international Convention on the Elimination of all forms of Discrimination Against Women (“CEDAW”) with changes successive New Zealand Governments have made to the status of women so as to discover the degree of intent such Governments have had to implement equality.
This thesis is in chronological order, beginning from an analysis of the creation of the status of women dating pre 1300 B.C., detailing degradations, changes and improvements in the status up until 2012 A.D. The main divisions are based on general periods of importance for women; chapter one investigates how the secondary status of women originated and evolved in ancient eras. Chapter two examines the significant international and domestic women’s rights movements during the mid-twentieth century. Chapter three discusses the importance of an international instrument as a comparative tool; illustrated by CEDAW’s contrast to the New Zealand status of women during the mid-1980s. Chapter four analyses the Governmental changes made over the next quarter century to discover whether New Zealand was moving closer towards a reflection of the international instrument. Chapter five evaluates the contemporary status of women in New Zealand; and finally, chapter six details recommendations for the State with the intention of raising the status of women to full equality.
The conclusions reached are, first; that the current status of women in New Zealand is not one of equality with men because their original status was seen as secondary. Therefore the goal of attaining equal (formal) legal rights to gain equality is not appropriate as it merely gives women what were considered “men’s rights” without giving them the opportunity to practice them in full equality. Secondly; the use of CEDAW as a comparative instrument is shown to provide a more effective strategy of gaining equality that does not always involve giving women gender-neutral “men’s rights” but needs to be given greater power to be proved effective.
The comparison with an instrument that provides for perfect equality contributes to a thorough understanding of the status of women in New Zealand as the comparison provides a clear and objective view of why the original premise that formal rights would achieve substantive equality was an incorrect supposition. The thesis also contributes alternative action to be undertaken by the Government to effectively achieve equality for women.

text: A Historical Analysis of the Status of Women in New Zealand: Has CEDAW had an Impact? This thesis analyses the current and historical status of women in New Zealand for the purpose of discovering why full equality between men and women has not yet been achieved. This object will be accomplished by analysing, comparing and contrasting the international Convention on the Elimination of all forms of Discrimination Against Women (“CEDAW”) with changes successive New Zealand Governments have made to the status of women so as to discover the degree of intent such Governments have had to implement equality.
This thesis is in chronological order, beginning from an analysis of the creation of the status of women dating pre 1300 B.C., detailing degradations, changes and improvements in the status up until 2012 A.D. The main divisions are based on general periods of importance for women; chapter one investigates how the secondary status of women originated and evolved in ancient eras. Chapter two examines the significant international and domestic women’s rights movements during the mid-twentieth century. Chapter three discusses the importance of an international instrument as a comparative tool; illustrated by CEDAW’s contrast to the New Zealand status of women during the mid-1980s. Chapter four analyses the Governmental changes made over the next quarter century to discover whether New Zealand was moving closer towards a reflection of the international instrument. Chapter five evaluates the contemporary status of women in New Zealand; and finally, chapter six details recommendations for the State with the intention of raising the status of women to full equality.
The conclusions reached are, first; that the current status of women in New Zealand is not one of equality with men because their original status was seen as secondary. Therefore the goal of attaining equal (formal) legal rights to gain equality is not appropriate as it merely gives women what were considered “men’s rights” without giving them the opportunity to practice them in full equality. Secondly; the use of CEDAW as a comparative instrument is shown to provide a more effective strategy of gaining equality that does not always involve giving women gender-neutral “men’s rights” but needs to be given greater power to be proved effective.
The comparison with an instrument that provides for perfect equality contributes to a thorough understanding of the status of women in New Zealand as the comparison provides a clear and objective view of why the original premise that formal rights would achieve substantive equality was an incorrect supposition. The thesis also contributes alternative action to be undertaken by the Government to effectively achieve equality for women.

year: 2013

title: The art of dialogue with indigenous communities in the new biotechnology world

authors: Hudson, Maui

subjects: biotechnology

abstract: Te Hau Mihi Ata is a research project that aims to negotiate spaces for and develop processes of dialogue that allow for a deeper level of interaction between mtauranga Māori (Māori indigenous knowledge) and science. Over a two-year period a series of facilitated exchanges or wnanga were held focusing on areas of new technology (assisted reproductive technologies, life technologies, and future food technologies) that involved Māori scientists and people with expertise in mtauranga Māori. These dialogue events were designed to explore, through the challenge of considering new biotechnologies, the similarities and differences that emerge from approaching these issues from different knowledge paradigms. This paper will outline the key project findings from this series of exchanges including the barriers and facilitators to the dialogue process and knowledge exchange as well as discuss how participants created connections between scientific discourse and indigenous knowledge frameworks.

text: The art of dialogue with indigenous communities in the new biotechnology world Te Hau Mihi Ata is a research project that aims to negotiate spaces for and develop processes of dialogue that allow for a deeper level of interaction between mtauranga Māori (Māori indigenous knowledge) and science. Over a two-year period a series of facilitated exchanges or wnanga were held focusing on areas of new technology (assisted reproductive technologies, life technologies, and future food technologies) that involved Māori scientists and people with expertise in mtauranga Māori. These dialogue events were designed to explore, through the challenge of considering new biotechnologies, the similarities and differences that emerge from approaching these issues from different knowledge paradigms. This paper will outline the key project findings from this series of exchanges including the barriers and facilitators to the dialogue process and knowledge exchange as well as discuss how participants created connections between scientific discourse and indigenous knowledge frameworks.

year: 2012