Influence of Partial Remelting and Holding on the Cast Structure of some Aluminum Alloys
Mahmoud Abdallah Ahmadein;
Abstract
Processing metal alloys in the semi-solid state, where they are worked in the mushy zone is a relatively new technology. This work is concerned with producing semi-solid slurries with best possible properties for consequent thixo-processing using partial remelting. Since the mushy state can be reached either by partial remelting, or by partial freezing, the latter have been investigated for comparison. The experimental work starts with preliminary investigations to select the suitable alloys, melting and casting conditions, design of the casting molds and
determination and control of the solid fraction for the produced billets.
Two aluminum alloys, AI-10%Cu and Al-5%Si, have been studied. The preliminary investigations showed that the former alloy suffers from macrosegregation and therefore, the main experiments were performed on the
• latter. Stainless steel molds of 1 mm wall thickness, 11 mm average diameter and
135mm height were prepared to suit tensile, hardness and micro-examination test
pieces. Modification of molten Al-5%Si with sodium salts was tried. The results showed that the globular structure after partial remelting and holding has not been affected. However, this treatment had been applied in all experiments for its
beneficial effect of eliminating inclusions and gases from the melt.
Based on the preliminary results the main experiments were conducted to study the effects of the following parameters on the microstructure, tensile and hardness properties of the alloy after partial remelting and holding:
- Initial cast-structure cooling rate at three values:25°C/s, 2.1 °C/s & 2.1 °C/min.
- Reheating rate at two values: 0.7C/min. and 18°C/min.
- Holding time, ranging from Oto 300 minutes.
- Holding temperature corresponding to solid fractions of: 0.3, 0.4, 0.5 & 0.6
In a comparative study, partial freezing and holding has been experimented as an alternative technique at 4.4°C/min. and 25°C/min. freezing rates .
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determination and control of the solid fraction for the produced billets.
Two aluminum alloys, AI-10%Cu and Al-5%Si, have been studied. The preliminary investigations showed that the former alloy suffers from macrosegregation and therefore, the main experiments were performed on the
• latter. Stainless steel molds of 1 mm wall thickness, 11 mm average diameter and
135mm height were prepared to suit tensile, hardness and micro-examination test
pieces. Modification of molten Al-5%Si with sodium salts was tried. The results showed that the globular structure after partial remelting and holding has not been affected. However, this treatment had been applied in all experiments for its
beneficial effect of eliminating inclusions and gases from the melt.
Based on the preliminary results the main experiments were conducted to study the effects of the following parameters on the microstructure, tensile and hardness properties of the alloy after partial remelting and holding:
- Initial cast-structure cooling rate at three values:25°C/s, 2.1 °C/s & 2.1 °C/min.
- Reheating rate at two values: 0.7C/min. and 18°C/min.
- Holding time, ranging from Oto 300 minutes.
- Holding temperature corresponding to solid fractions of: 0.3, 0.4, 0.5 & 0.6
In a comparative study, partial freezing and holding has been experimented as an alternative technique at 4.4°C/min. and 25°C/min. freezing rates .
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Other data
| Title | Influence of Partial Remelting and Holding on the Cast Structure of some Aluminum Alloys | Other Titles | تأثير الصهر الجزئى والإحتفاظ على بنيان بعض سبائك الألومنيوم المصبوبة | Authors | Mahmoud Abdallah Ahmadein | Issue Date | 2003 |
Attached Files
| File | Size | Format | |
|---|---|---|---|
| B15755.pdf | 1.05 MB | Adobe PDF | View/Open |
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