A Study of Rapidly Solidified Al1.5wt%/3wt%Mg0.2wt%Sc Powders and Strips using Impulse Atomization

• Author / Creator

  Yin, Shengze

• In this work, rapid solidification microstructures and mechanical properties of Al1.5Mg0.2Sc and Al3Mg0.2Sc are investigated. Samples in the form of powders and strips / deposits of different thermal histories are obtained by means of impulse atomization technique. Cooling rates of the powders, varying from 300K/s to 900K/s within the investigated size range, are estimated using a thermal model of a solidifying droplet in a stagnant gas. Whereas cooling rates of the strips are measured by a two-color pyrometer at the strip-substrate interface and is found to average 1.7K/s. The effects of Mg content, cooling rate and melt superheat on the scale of microstructures and mechanical properties are investigated. The role of Sc is also analyzed. The increase in Mg content and cooling rate are found to yield finer microstructures. For both powders and strips, a reduction in cell spacing is found to have limited impacts on microhardness. However, increasing Mg content (from 1.5wt% to 3wt %) is found to have a strengthening effect estimated by a hardness value of about 20 HV0.1. While cell spacing of the powders is found to increase with melt superheat, no noticeable difference in cell spacing or microhardness is observed. The effects of heat treatment on mechanical properties is also investigated. Aging of the as-atomized powders and strips are carried out at 300 °C for up to 2 hours in a DSC. Microhardness is measured on both as-atomized and aged samples. Maximum hardness is reached for both powders and strips after 2 hours of aging. For both alloy compositions compositions, a hardness increase of 40 HV0.1 is obtained. From DSC results and phase diagram, Sc precipitation is found to be responsible for the aging response. Compared with published industrial data on cooling rate, cell spacing, and response to aging, the combinations of the impulse atomization and impulse atomization with spray deposition exhibit the possibility of being used as a small scale platform for novel alloys testing and development for industrialized rapid solidification processes, such as twin-belt strip casting process.

• Subjects / Keywords

  • Powders
  • Impulse Atomization
  • Spray Deposition
  • Rapid Solidification
  • Age Hardening
  • Al-Mg-Sc Alloy
  • Strips

• Graduation date

  Fall 2016

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3CZ32C95

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.