Dry Sliding Friction and Wear Properties of Al–25Zn–3Cu–(0–5)Si Alloys in the As-Cast and Heat-Treated Conditions

Dry sliding friction and wear properties of ternary Al–25Zn–3Cu and quaternary Al–25Zn–3Cu–(1–5)Si alloys were investigated using a pin-on-disc test machine after examining their microstructures and mechanical properties. An alloy (Al–25Zn–3Cu–3Si), which exhibited the highest tensile and compressive strengths, was subjected to T7 heat treatment. Surface and subsurface of the wear samples were investigated using scanning electron microscopy (SEM). The hardness and both tensile and compressive strengths of the alloys increased with increasing silicon content, but the trend reversed for the latter ones above 3% Si. It was observed that T7 heat treatment reduced the hardness and both tensile and compressive strengths of the Al–25Zn–3Cu–3Si alloy, but increased its elongation to fracture greatly. Three distinct regions were observed underneath the surface of the wear samples of the Al–25Zn–3Cu–3Si alloy. The formation of these regions was related to the heavy deformation of surface material and mixing, oxidation and smearing of wear material. Al–25Zn-based ternary and quaternary alloys in both as-cast and heat-treated conditions were found to be superior to SAE 660 bronze as far as their mechanical and dry sliding wear properties are concerned.     

Measurement of electromagnetic radiation with respect to the hours and days of a week at 100kHz–3GHz frequency band in a turkish dwelling

In this paper, the electromagnetic (EM) radiation to which we are exposed in our life is aimed to be observed during a week. The measurements are carried out in a randomly selected apartment during 24 h a day at 4 s sampling period for all days of a week. Due to the result of the study, we can see whether any radiation above specified limits occurs during a day and week or not and also we can determine how an ordinary instantaneous measurement represents the usual radiation level in related area. Measurement results showed that EM radiation levels in 100 kHz–3 GHz frequency band were considerably below specified limit values. There is statistically no difference between measured values in Monday and Saturday with respect to days. However, it is observed that the measured values in other days except for Monday and Saturday are statistically considerably different.