טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentEsther Karbian Kiperwasser
SubjectPlasma Treatment Casting (PTC) Process Influence
on Microstructure of Aluminium 6063
DepartmentDepartment of Materials Science and Engineering
Supervisor Professor Emeritus Bamberger Menachem
Full Thesis textFull thesis text - English Version


Abstract

The Plasma Treatment Casting (PTC) process is an advanced stirring process that stirs molten metals and alloys during the solidification in conductive and nonconductive dies. The intensive stirring has several major benefits: finer microstructure, better chemical homogeneity and more efficient feeding in both macro and micro scales.

Today’s casting industry is continuously pursuing methods for improving casting quality, time, energy and material conservation, which together lead to cost reduction and environmental benefits.

Direct-chill (DC) casting is currently the most common semi-continuous casting practice in the production of 6063 wrought aluminum alloys. This method results in a coursed and non-homogenous microstructure. It requires homogenization treatment to follow the casting in order to allow 6063 Aluminum DC cast billets workability in extrusion and required mechanical properties.

This study focused on investigating the aluminum 6063 microstructure formed while PTC is applied during the DC casting, and its influence on the exrtrudability and mechanical properties of the final extruded profiles.

The study revealed that the PTC treated samples exhibit very fine microstructure, which is very similar to the homogenized samples in comparison to the As-Cast, and in addition high extrudability and mechanical properties.

Microstructure refinement found in PTC treated billets, was suspected to be due to an increased cooling rate, which was a result of the effective heat transfer increase ensuing from the stirring effect. Competitive growth and/or competitive nucleation cause the β phase to be suppressed by the a phase at high cooling rates. Similar, the a phase is suppressed by the β phase at lower cooling rates - thus the transformation αAlFeSi->βAlFeSi was suppressed in PTC treated billets. In addition, the fine microstructure was a result of the stirring effect that breaks the dendrites tips and creates new nucleation sites. α AlFeSi phase contains less silicon than the βAlFeSi phase and has more globular and fragmented morphology, thus the formation of α AlFeSi phase increases the ductility of the material. In addition, the remaining Si created the hardening fine precipitates of β MgxSiy during the aging process, which function as encores for dislocations movement and creates a hardening effect in the material. Furthermore,  the PTC treated billets' refined microstructure and smaller DAS have a strong influence on decreasing defects rate and improving PTC cast billet soundness in comparison to the As-Cast.