Slope plate casting of hypereutectic al-sialloy

Dissertant

Abd, Usamah Ibrahim

Thesis advisor

Abd al-Latif, Nawal Izzat

University

University of Technology

Faculty

-

Department

Department of Production Engineering and Metallurgy

University Country

Iraq

Degree

Master

Degree Date

2011

English Abstract

-The aim of this work was to study effect of Slope plate casting (SPC) process on the microstructure of a hypereutectic Al-23%Si alloy, i.e., on refining and modification of primary Si and eutectic phases.

In this work, slope plate casting unit was manufactured.

Effects of the overheating temperature and tilt angle on the microstructure and hardness of a hypereutectic Al-23%Si alloy were investigated.

Therefore, the melt was overheated to (760, 790, 820 and 850) ºC and poured onto slope plate continuously cooled with water circulation underneath, with various tilt angles (40, 50, 60)º using a constant cooling length (300 mm).

After, the melt became a semi-solid, the slurry was then filled the mould and completely solidified.

Slope plate samples were reheated to a semi-solid temperature (550)ºC for (10 min) and then quenched in water, to study the effect of reheating on the microstructure and hardness of a hypereutectic Al-23%Si alloy.

Optical Microscopy and Scanning Electron Microscopy (SEM) were employed to characterize slope plate casting samples before and after reheating to the semi-solid temperature.

The results showed that the overheating temperature and tilt angle of slope plate affect the size and morphology of primary silicon (β-Si) phase.

Images analysis showed that the grain size and the shape factor of (β-Si) phase were decreased with increasing of the overheating temperature and tilt angles, on other hand, the volume fraction of (β-Si) phase was increased.

The minimize grain size at 850 ºC and all tilt angles (40, 50, 60)º was obtained, where the values of grain size of (β-Si) phase are (approximately ٢١.٦, 18.5 and ١٦ μm) and a shape factor (1.5, 1.38 and 1.36) at these conditions, respectively, as compared with the grain size (123 μm) and the shape factor (2.73) for ascast alloy.

The results of microstructural observations showed that SPC process contributed to change the eutectic Si phase morphology of hypereutectic Al-23%Si alloy from a needle-like structure to fibrous structure distributed around (α-Al) phase, the aspect ratio of the eutectic structure was decreased with increase of the overheating temperature and tilt angles.

The results of the reheating route showed that the grain size of (β-Si) phase was slightly increased after reheating at all overheating temperatures and tilting angles.

On other side, the shape factor was improved, and the volume fraction of (β-Si) phase was decreased, as compared with slope plate results.

Also, the fibrous eutectic in the slope plate microstructures was changed to a fine fibrous (discontinuous) or nearly a globular eutectic structure after reheating.

The results of hardness tests showed that the hardness of SPC-samples was decreased with increase of the overheating temperature, and there is no major change in hardness with increase of tilt angle.

After reheating to the semi-solid temperature, the hardness was decreased with increase of the overheating temperature at constant tilt angle.

Design of experiments was used to optimize the process parameters before and after reheating and indicate the optimum ones.

The ANOVA results predicted two mathematical models for the (β-Si) grain size (before and after reheating, Y1 and Y2, respectively), as follow: Y = 2913.42−2.48×A−6.72×B−0.02×A +0.01×AB Y = 2909.53−3.21×A−6.66× B−0.01 ×A The results of design of experiments indicated that the optimum setting was (833.636)ºC pouring temperature and (60º) tilt angle with grain size (15.7238 μm), and (835.455)ºC pouring temperature and (60º) tilt angle with grain size (18.2937 μm) for before and after reheating, respectively.

Main Subjects

Materials Science , Minerals

Topics

• Temperatures
• Alloys

• APA
• MLA
• AMA

Language

English

Data Type

Arab Theses

Record ID

BIM-305154