Rafiq A. Siddiqui

Influence of aging parameters on the mechanical properties of 6063 aluminium alloy

Abstract The 6063 aluminium alloy were given various heat treatments at under-aged, peak-aged and over-aged temperatures. The effect of precipitation on the tensile strength, yield strength, hardness, ductility and number of cycles required to fail the alloy at constant stress was investigated. The variation in time and temperature have improved the mechanical properties of the Al-alloy, whereas the ductility has decreased. The experimental work has revealed that time and temperature play a very important role in the precipitation hardening process of the Al-alloy. The initial increase in the tensile strength, yield strength, hardness and fatigue is due to vacancies assisted diffusion mechanism and formation of high volume fraction of guinier preston (GP) zones, which disturbs the regularity in the lattices. In over-aging of the alloy, the size of the individual particle increases, but the number of particles decreases. This causes few obstacles to the movement of dislocations, therefore, the mechanical properties decreases. The scanning electron microscope (SEM) study of the under-aged alloy have exhibited facet fatigue fracture surface, whereas the peak-aged and over-aged alloy show a mixed mode of fracture, i.e. facet fracture with striation and also intergranular fracture.

Modeling of nitrogen oxides (NOx) concentrations resulting from ships at berth

Oxides of nitrogen (NOx) emissions from ships (marine vessels) contribute to poor air quality that negatively impacts public health and communities in coastal areas and far inland. These emissions often excessively harm human health, environment, wildlife habituates, and quality of life of communities and indigenous of people who live near ports. This study was conducted to assess the impact of NOx emissions origination from ships at berth on a nearby community. It was undertaken at Said Bin Sultan Naval base in Wullayat Al-Mussana (Sultanate of Oman) during the year 2005. The Industrial Source Complex Short Term (ISCST) model was adopted to determine the dispersion of NOx into port and beyond into surrounding urban areas. The hourly and monthly contours (isopleths) of NOx concentrations in and around the port were plotted. The results were analyzed to determine the affected area and the level of NOx concentrations. The highest concentration points in the studied area were also identified. The isopleths of NOx indicated that most shipping emissions of NOx occur at the port can be transported over land. The output results can help to derive advice of recommendations ships operators and environmentalists to take the correct decision to prevent workers and surrounded environment from pollution.