الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Since the origin of the Earth, its crust contains naturally occurring radionuclides randomly distributed with different activity concentrations all over the earth. These primordial radionuclides have sufficiently longer half-lives and decaying to attain the stable state by producing ionizing radiation in various degrees. The wide range of the spread of radioactive elements in the earth’s crust showed the need for measuring radioactivity to avoid the hazards of exposing to the radiation, especially when handling raw materials used in industry.Soldering process is the most important and oldest processes that many industries depend on them especially for metal interconnections, the origins of this process dating back to 2,000 years ago where Sn-Pb alloys dominates the solders used in manufacture because of their unique combination of material properties, such as low cost, availability, low melting temperatures, ductility and excellent wetting on Cu and its alloys.In addition to the possibility of the presence of radiological risks, the toxicity of lead to people’s health and the environment is also a matter of concern, so, Japan and the European Union puts a legislations to eliminate the use of lead in soldering operations, which led to the appearance of a new alloys named as lead free solder alloys. These lead-free solders need to meet a series of standards such as: good wettability, low melting point, low cost and adequate strength. A number of investigations had been carried out on such promising lead-free solder alloys as Sn-Ag, Sn-Ag-Cu, Sn-Cu, Sn-Bi and Sn-In.Sn-Zn solder system is one of these alloys that are a suitable lead free solder because it has relatively low melting temperature and its mechanical properties. Also it has some disadvantages such as poor wetting and oxidation resistance.In this study, the natural activities of radionuclides, heavy metals, other poisonous elements and the effects of 0.5Cu and 1.5Cu additions on the microstructure, thermal behavior and tensile properties of Sn-6.5Zn alloys were investigated. The activities due to radioactive nuclei were examined by High Purity Germanium Detector (HPGe). X-ray Fluorescence (XRF) were used to analyze the elements in the investigated samples. The microstructure was examined by X-ray Diffractometer (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer (EDS). The thermal behaviors of the three solder alloys have been studied by using the differential scanning calorimetry (DSC). Tensile stress-strain test were performed at constant temperatures 25, 70 and 110 ℃and different strain rates ranging from 5.0*10^(-5) to 2.9*10^(-3) s^(-1)to determine the effect of 0.5Cuand 1.5Cuadditions on the mechanical properties of the examined alloy.Results showed that:It was found that the gamma-ray spectroscopic analysis of Sn-6.5Zn and Sn-6.5Zn-1.5Cu samples indicates the presence of natural radioactive isotopes with somewhat low activity, as well as three ones with fairly higher activity of 996.54, 573.59 and 110.81 Bq correspondent to Zn-65, Co-60 and K-40, respectively were found in Sn-6.5Zn sample, also three ones with fairly higher activity of 970.69, 488.72 and 112.26 Bq correspondent to Eu-152, Co-60 and K-40, respectively were found in Sn-6.5Zn-1.5Cu sample.Overall, the current results are mostly within the worldwide range of values found in Sn-6.5Zn and Sn-6.5Zn-1.5Cu alloy material samples, and this range is within the safe limits given in the report issued by United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR, 1993). Also, investigations reveal that the plain Sn–6.5Zn solder exhibitslarge number of undesirable acicular structure of angular needle-like Zn particles at the solder matrix.The acicular-shape morphology of Zn was remarkably suppressed after Cu modification. Moreover, anew type of small flower-like γ-Cu_5 Zn_8 intermetallic compound (IMC) was detected with 0.5 wt. % Cuadded specimens. The flower-like morphology of γ-Cu_5 Zn_8IMC appears to cause a sharp increase inYoung’s modulus, yield strength (YS) and ultimate tensile strength (UTS) of Cu modified solder.However, this effectiveness is reduced when 1.5 wt. % Cu addition starts to enhance the growth of coarsedendrite morphology of γ-Cu_5 Zn_(8 )phase with enlarged β-Sn matrix.The DSC results showed that the addition of 1.5 wt. % Cu was found to induce undesirable effects on the degree of melting point (had two endo-thermal peaks during heat at 200.6 and 214.5℃), pasty range (20.5℃) and undercooling (8.6℃).The experimental results of the tensile stress-strain tests for Sn-6.5Zn, Sn-6.5Zn-0.5Cu and Sn-6.5Zn-1.5C solder alloys points to some exclusive features for the tensile behavior of solders. The tensile specimens of Sn–6.5Zn–xCu solders experience simultaneous work hardening and dynamic recovery when they are deformed. The former hardens the solders, while the latter leads to strain softening caused by thermal activated process owing to the low (Tm) of Sn– 6.5Zn–xCu solders. It is seen that the stress levels decreased with increasing temperature at constant strain rate, whereas the elongation is decreased and increased with inconsistent behavior. Whereas the ductility of Sn–6.5Zn–0.5Cu solder is only 12.3% lower than the plain solder. Conversely, the addition of 1.5% Cu has a little influence on the tensile strength and Young’s modulus of Sn–6.5Zn solder. But the elongation of the Sn–6.5Zn solder deteriorates remarkably after1.5% Cu addition. The improvement in both tensile strength and ductility of Sn–6.5Zn–xCu solders is mainly depend on the shape and size of phase structure, and composition of alloy solders, which played a significant role for controlling the mechanical behavior.