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: An investigation of the factors affecting guest selection of hotel/motel accommodation within New Zealand: development of a management decision model

authors: Lockyer, Tim

abstract: This research investigates the factors that influence the selection of hotel/motel accommodation in New Zealand. The tourism and hospitality industries are an important part of the New Zealand economy, with tourism producing more overseas income than any other individual industry. It is vitally important for hotel and motel owners and management to understand the factors that affect occupancy in order that they may implement decisions to take best advantage of the assets and obtain the highest return on the investment. A holistic approach or one that looks at the many factors influencing hotel occupancy has been adopted as this encourages an interdisciplinary method to the study of hotel occupancy, and broadens the investigation. This gives the research a particular focus on the problem of occupancy because the analysis includes an extensive spectrum of factors. 

The specific objective is to investigate the factors that influence occupancy and to produce the findings in the form of a management decision model. The data for this research was gathered from three sources: first a small group of researchers and industry stakeholders participated in-depth interviews, which comprised open questions asked to determine from their perspective the factors that have the greatest affect on occupancy. The main findings from these interviews were used to develop a survey conducted among hotel decision-makers; management was specifically chosen for this, as it was believed that there would be a broader knowledge and experience base. The final set of data was collected from a survey of potential guests. 

In developing the management decision model, a number of tools were employed including neural networks and linear structural equation modelling. These analyses gave a rich result to the findings and this was applied to the development of stochastic¹ management decision models (Goel & Richter-Dyn, 1974; Bekker & Saayman, 1999), using the main findings from the interviews with researchers and industry stakeholders as a reference point. 

The contribution of this research included evidence of: 1). The significant “Gap” between the factors influencing occupancy relating to researchers and industry stakeholders and hotel decision-makers on the one hand and potential guests on the other; 2). The structure and factors involved within a hotel occupancy decision model; 3). The demographic influences on the factors within the management decision model. 

¹The way in which the variables within the model relate and impact on each other.

text: An investigation of the factors affecting guest selection of hotel/motel accommodation within New Zealand: development of a management decision model This research investigates the factors that influence the selection of hotel/motel accommodation in New Zealand. The tourism and hospitality industries are an important part of the New Zealand economy, with tourism producing more overseas income than any other individual industry. It is vitally important for hotel and motel owners and management to understand the factors that affect occupancy in order that they may implement decisions to take best advantage of the assets and obtain the highest return on the investment. A holistic approach or one that looks at the many factors influencing hotel occupancy has been adopted as this encourages an interdisciplinary method to the study of hotel occupancy, and broadens the investigation. This gives the research a particular focus on the problem of occupancy because the analysis includes an extensive spectrum of factors. 

The specific objective is to investigate the factors that influence occupancy and to produce the findings in the form of a management decision model. The data for this research was gathered from three sources: first a small group of researchers and industry stakeholders participated in-depth interviews, which comprised open questions asked to determine from their perspective the factors that have the greatest affect on occupancy. The main findings from these interviews were used to develop a survey conducted among hotel decision-makers; management was specifically chosen for this, as it was believed that there would be a broader knowledge and experience base. The final set of data was collected from a survey of potential guests. 

In developing the management decision model, a number of tools were employed including neural networks and linear structural equation modelling. These analyses gave a rich result to the findings and this was applied to the development of stochastic¹ management decision models (Goel & Richter-Dyn, 1974; Bekker & Saayman, 1999), using the main findings from the interviews with researchers and industry stakeholders as a reference point. 

The contribution of this research included evidence of: 1). The significant “Gap” between the factors influencing occupancy relating to researchers and industry stakeholders and hotel decision-makers on the one hand and potential guests on the other; 2). The structure and factors involved within a hotel occupancy decision model; 3). The demographic influences on the factors within the management decision model. 

¹The way in which the variables within the model relate and impact on each other.

year: 2001

title: Pātangaroa: Co-developing management strategies for a starfish outbreak in Ōhiwa Harbour

authors: Ranapia, Megan

subjects: marine management

abstract: The management of marine environments often prioritises scientific information to address complex marine social-ecological issues. However, there is a wealth of learning to be gained from Indigenous people who have generated place-based intergenerational understandings and cultural ethics and practices. Consequently, Indigenous knowledge alongside science can offer better insights, holistic understanding, sustainable management strategies and greater sources of evidence. This research is located in Aotearoa New Zealand and engages in mātauranga Māori (Māori knowledge) alongside marine ecology as an appropriate method for contemporary marine research and management. The thesis study focused on Ōhiwa Harbour, aiming to co-develop a starfish management action plan (SMAP) with local iwi (tribe) Ngāti Awa and other affiliated iwi, district councils and regional council to address the overabundant starfish (species: Coscinasterias muricata and Patiriella regularis). By engaging in transdisciplinary research and collaborative decision-making, this study sought to bridge the gap between Indigenous knowledge and mainstream science, offering lessons for inclusive marine management practices.

To achieve this, I developed and prescribed a co-developed framework actively promoting a mixed-methods approach, inclusive of kaupapa Māori research methodologies, tikanga, participatory design, applied mātauranga ā iwi, quantitative marine scientific field methods and experimental study design. Through the collaborative process, I identified areas of appropriate research aims and methods. This included co-developing a novel starfish trapping methodology sensitive to local ecology and cultural values and an experimental starfish removal study to assist decision-makers in implementing an efficient and effective starfish removal regime as an approach to management.

Results from the field studies showed the efficacy of starfish traps is dependent on environmental conditions, physical characteristics and soaking time (the length of time the trap is left in the water). A soaking time of 48 h maintained the highest starfish catch per unit effort (CPUE) while minimising time to re-bait and reset traps. Observations also indicated an open trap design had less bycatch than a semi-enclosed box trap and could withstand the tidal currents for a longer period. The findings found that bait type did not impact on CPUE. In the starfish removal study, the combined effort of diver removals and trapping produced higher daily catch rates than the single treatments (i.e., diver removals only or trapping only), therefore was themost efficient removal method. The empirical information gathered from the field studies was then used to inform the SMAP and was accepted unanimously at the highest local/regional co-management level. Furthermore, through the findings I identified future research opportunities that would further close gaps in our knowledge around the best management approaches for a starfish outbreak. These included investigation into the predation impacts of P. regularis on mussel recruitment, identification of alternative restoration sites less susceptible to starfish predation pressures and investigation of potential drivers of the starfish outbreak.

Overall, the acceptance of the SMAP by local iwi/hapū and government authorities underscores the success of the collaborative approach. The collaborative process not only addresses the immediate concerns of starfish infestation but contributed to the broader goal of supporting kaitiakitanga (active guardianship) responsibilities and promoting Indigenous perspectives in marine management. This thesis demonstrates and recommends a new approach to starfish management in coastal marine areas using both marine science and mātauranga Māori understandings, practices and ethics, furthermore, it demonstrates the commitment to the inclusion of multiple knowledge systems and involvement of communities.

text: Pātangaroa: Co-developing management strategies for a starfish outbreak in Ōhiwa Harbour The management of marine environments often prioritises scientific information to address complex marine social-ecological issues. However, there is a wealth of learning to be gained from Indigenous people who have generated place-based intergenerational understandings and cultural ethics and practices. Consequently, Indigenous knowledge alongside science can offer better insights, holistic understanding, sustainable management strategies and greater sources of evidence. This research is located in Aotearoa New Zealand and engages in mātauranga Māori (Māori knowledge) alongside marine ecology as an appropriate method for contemporary marine research and management. The thesis study focused on Ōhiwa Harbour, aiming to co-develop a starfish management action plan (SMAP) with local iwi (tribe) Ngāti Awa and other affiliated iwi, district councils and regional council to address the overabundant starfish (species: Coscinasterias muricata and Patiriella regularis). By engaging in transdisciplinary research and collaborative decision-making, this study sought to bridge the gap between Indigenous knowledge and mainstream science, offering lessons for inclusive marine management practices.

To achieve this, I developed and prescribed a co-developed framework actively promoting a mixed-methods approach, inclusive of kaupapa Māori research methodologies, tikanga, participatory design, applied mātauranga ā iwi, quantitative marine scientific field methods and experimental study design. Through the collaborative process, I identified areas of appropriate research aims and methods. This included co-developing a novel starfish trapping methodology sensitive to local ecology and cultural values and an experimental starfish removal study to assist decision-makers in implementing an efficient and effective starfish removal regime as an approach to management.

Results from the field studies showed the efficacy of starfish traps is dependent on environmental conditions, physical characteristics and soaking time (the length of time the trap is left in the water). A soaking time of 48 h maintained the highest starfish catch per unit effort (CPUE) while minimising time to re-bait and reset traps. Observations also indicated an open trap design had less bycatch than a semi-enclosed box trap and could withstand the tidal currents for a longer period. The findings found that bait type did not impact on CPUE. In the starfish removal study, the combined effort of diver removals and trapping produced higher daily catch rates than the single treatments (i.e., diver removals only or trapping only), therefore was themost efficient removal method. The empirical information gathered from the field studies was then used to inform the SMAP and was accepted unanimously at the highest local/regional co-management level. Furthermore, through the findings I identified future research opportunities that would further close gaps in our knowledge around the best management approaches for a starfish outbreak. These included investigation into the predation impacts of P. regularis on mussel recruitment, identification of alternative restoration sites less susceptible to starfish predation pressures and investigation of potential drivers of the starfish outbreak.

Overall, the acceptance of the SMAP by local iwi/hapū and government authorities underscores the success of the collaborative approach. The collaborative process not only addresses the immediate concerns of starfish infestation but contributed to the broader goal of supporting kaitiakitanga (active guardianship) responsibilities and promoting Indigenous perspectives in marine management. This thesis demonstrates and recommends a new approach to starfish management in coastal marine areas using both marine science and mātauranga Māori understandings, practices and ethics, furthermore, it demonstrates the commitment to the inclusion of multiple knowledge systems and involvement of communities.

year: 2025-05