2017-05-11 15:37:20

Aluminum alloy castings

Behavior of Aluminum Alloy Castings under Different Pouring Temperatures and Speeds

Abstract
The investigation studies the effect of pouring temperatures and rates on the mechanical properties of Aluminum alloy castings. The castings were produced at different pouring temperatures and speeds. The speed range is 2.0 cm/s to 16.0 cm/s, while the temperature range for the investigation is 680oC to 750oC. The specimens were subsequently tested for quality and properties such as hardness and strength. Observations and results indicated that lower pouring temperatures, nearer to the melting temperatures of the alloys produced good quality castings with the optimum values of hardness and strength as 65.5 and 112 N/mm2 respectively. The optimum pouring speed is in the range of 2.2 cm/s to 2.8cm/s, where the hardness and strength were 65.4 and 127 N/mm2 respectively.
Keywords

Pouring Temperature; Pouring Speed; Ultimate Tensile Strength; Rockwell Hardness; Percentage Elongation; Percentage Reduction in Area.

Introduction
To an engineer, the knowledge and understanding of casting parameters in casting different metals and alloys is as significant as the cast products. Metal casting is by definition any process of melting metal and pouring them into mould in order to produce the required shapes. Specific casting parameters such as pouring temperatures, rate of pouring, fluidity and composition of metals are of topmost importance for consideration if sound casting is to be achieved.

It has been observed [1] that melting and pouring conditions directly or indirectly affects such mechanical properties of cast materials as: hardness, percentage elongation, percentage reduction in diameter, toughness and so on. For instance an investigation on pouring rate of some ferrous metals [2] revealed that metals such as steels have very high freezing rate compared to most other alloys castings. The optimum pouring speed is also found to be a function of the casting size and shape.

The knowledge of melting temperature of metals and alloys is necessary to estimate their corresponding pouring temperature [3]. Aluminum alloy casting has melting temperature of 660°C [4] with its corresponding pouring temperature range to be between 700°C-750°C. It was also stated by Lindberg [5] that this melting temperature may be as low as 649°C.

In this paper, the efforts made in ‘sand casting’ Aluminum alloy of the same size and shape at selected pouring temperatures and rates is presented. The cast alloys were examined for mechanical properties. The aim is to determine the optimum points at which these parameters produce good quality castings. It has been stated [6] that when pouring temperature is lower than optimum, the mould cavity will not fill the gate or riser will solidify too rapidly and intercept directional solidification. On the other hand, higher pouring temperature causes shrinkage of the casting and mould warping [7]. Above all, many casting defects result because the optimum casting conditions were not used during the casting process

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