Studying the Effect of Adding Up To 6wt%Cu on Some Mechanical and Physical Properties of Pure Aluminum

Aluminum and its alloys solidify in columnar structure with large grain size which results in deterioration of their surface quality and strength. Aluminum alloys with a wide range of properties are used in engineering structures. Copper has been the most common alloying element almost since the beginning of the aluminum industry, and a variety of alloys in which copper is the major addition were developed. In this work, the influence of pure copper addition to commercially pure aluminum hardness, compression strength and thermal conductivity were studied. Six different Al-Cu alloys with 1,2,3,4,5 and 6%Cu content were prepared and experimentally tested. It was found that adding up to 6wt%Cu led to linear increasing in Brinell hardness, compression strength and slightly increasing in the thermal conductivity of aluminum-copper alloys.


INTRODUCTION
Aluminum and aluminum alloys are gaining huge industrial significance because of their outstanding combination of mechanical, physical and tribiological properties over the pure aluminum. These properties include high specific strength, high wear seizure resistance, high stiffness, better high temperature strength, controlled thermal expansion coefficient and improved damping capacity [1]. Aluminum is the second widely used metal due to its describable chemical, physical and mechanical properties and it represents an important category of technical materials [2]. Due to its high strengthtoweight ratio, besides other desirable properties e.g. desirable appearance, non-toxic, non-sparking, non-magnetic, high corrosion resistance, electrical and thermal conductivities and ease of fabrication, aluminum and its alloy are used in a wide range of industrial applications for different aqueous solutions. These properties led also to the association of aluminum and its alloys with transportation particularly with aircraft and space vehicles construction and building, containers and packaging and electrical transmission lines [3]. Mechanical properties of Al-Cu alloys depend on copper content. Copper is added to aluminum alloys to increase their strength, hardness, fatigue strength, creep, resistance and machinability. The first and most widely used aluminum alloys were those containing 4 -10 Wt% Cu [4]. Copper is being used, due to its relatively high solubility in aluminum [5]. Thus, (Al-Cu) solid solution matrix that is mechanically tougher than a pure (Al) matrix [6]. The grain size is obviously a function of several parameters, the most important of which are the nucleation rate and the growth rate. the nucleation rate depends on the amount of energy required for the creation of a new phase structure and melt under cooling below the liquids (which gives a direct thermodynamic stimulus for nucleation, decreasing the critical size of the solidification nucleus), and or by the presence of solidification sites for heterogeneous nucleation (that provide the suitable surface for nucleation, decreasing the amount of required energy)[7].
In this paper the influence of copper on hardness, compression strength and thermal conductivity were studied.
The following paragraphs provide a summary of studies on the effect of adding copper on the microstructures, mechanical properties and thermal conductivity of pure aluminum.

Casting Materials:
Different samples of Al-Cu Alloys were used in this work. The base material used throughout this work was the commercial pure aluminum of 99.9Wt% Al, pure copper with 99.9 % purity was used as an alloying element. Six alloys with different weight percentage copper were prepared, i.e. (1, 2, 3, 4, 5 and 6Wt% Cu).

Equipment and Experimental:
The following machines and equipment's were used: a) Sensitive balance device three digits.

The Specimen Were Prepared Through Gravity Casting Process:
a) Weighing the alloying elements by using sensitive balance with accuracy (0.001g).
b) The melting procedure was firstly performed by melting aluminum, using graphite crucible which was preheated in an electrical furnace, then the addition of copper element was carried out at (750 o C).

c)
During the addition of copper to the molten aluminum manual stirring for (10 seconds) with graphite rod with diameter (2.5 cm) was applied carefully to avoid producing too much dross.
d) The mold drilled with (2mm ) diameter in the upper and lower position of the mold to fit the first thermocouple sensor to be in contact with molten alloy and the second one was positioned in the lower part of the mold body and the steel casting mold dimension is shown in Fig. (1) .

e)
Pouring the molten alloys in to steel mold as shown in Fig. (2) , then leaving the casting to cool to the room temperature and digital camera was used to record the temperature readings, because of difficulty of recording the temperature drop in the start of casting alloys.
f) Six casting of aluminumcopper were manufactured with different addition. The preliminary chemical composition is given in Table (1 3) shows part of (Al-Cu) equilibrium phase diagram. It is observed that the maximum solubility of Cu in Al is (5.65%) at (548 ºC) and is reduced to (0.1%) at room temperature. So normal casting processes as in the present study should led to the formation of (CuAl2).
Moreover, Fig. (3) reveals that the solidification temperature of (Al-Cu) alloys is a function of Cu content. It was observed from the results, that the time -temperature curve, illustrated in

Thermal Conductivity:
Thermal conductivity of the (Al-Cu) alloys is in direct relationship with the Wt%Cu addition which shown in Fig. (6

Compression Strength:
In compression strength test for the (Al-Cu) alloys which were used in this work the minimum value was (70Mpa) for (99Wt%Al-1Wt%Cu) and the maximum value was (150Mpa) for (94Wt%Al-6Wt%Cu). Fig. (7) shows the relation between the compression strength and the copper content. This behavior can be attributed to the solid solution hardening mechanism and to the presence of hard (Al 2 Cu) particles dispersed in the alloy.

2.
The copper addition caused linear increasing in the hardness, compression strength and thermal conductivity of the (Al-Cu) alloys.