Dynamic Crystallization: An Influence on Degree of Prior Deformation and Mechanical Strength of 6063 Aluminum Alloy
This research is aimed at investigating the influence dynamic solidification of melts on degree of mechanical deformation and mechanical strength of 6063 aluminum alloy. Cylindrical samples of 14mm diameter and 140mm long were die cast following two techniques – vibration and static. Prior deformation via forging was imposed on each solidified sample to achieve 7%, 14%, 21% and 28% thickness reductions respectively for each casting technique. Average deformation load, average hammer velocities and the average energy absorbed were recorded. Tensile properties of each sample were studied via the use of Monsanto tensometer. Mechanical agitation of mould and its content increased the machinability of the alloy even at higer pre deformation. This was justified by the failure of the 28% reduction sample cast on static floor during machining to a tensile piece. The energy absorbed during deformation influences the tensile strength of the material. This increases with increase in percentage deformation except for 28% reduction whose magnitude was lower than that subjected to 21% reduction; vibrated samples possessed superior properties. From results obtained, vibrating a sample and subjecting to 21% pre-deformation possessed the best tensile strength.
Improvement on the strength of 6063 aluminum alloy by means of solution heat treatment
The paper examines the solution heat treatment of an extruded 6063 aluminum alloy. The study shows that the strength and fracture resistance of this metal alloy can be influenced to an appreciable extent by the solution heat treatment used in this investigation. The ultimate tensile strength (UTS) increases as the solution time increases from 6 to 20 hours for treatment temperature of 90C. The maximum UTS (198.8MPa and 188.6 MPa) occur at 120C and 150C respectively at the solution holding time of 10hours. While, at 120C and 10hrs, the UTS are relatively the same as the as-received specimen, though the latter exhibits a higher fracture stress. Annealing at 470C results to lower UTS value (114.3MPa) and poor fracture resistance (522MPa). The results of the experiment are found to be in near perfect agreement with Voce Empirical Model. These observations have shown that solution treatment at 150C for 10 hrs can produce significant plastic flow before fracture of 6063 aluminum alloys. Irrespective of the treatment process adopted, the stressstrain behavior is essentially the same for strains within the range 0 0.005. Materials Processing Challenges for the Aerospace Industry Organized by L.L. Shaw, S.L. Semiatin, R.F. Mignogna, and J.P. Singh Materials Science and Technology (MS&T) 2006: PROCESSING
Human Rights Obligations and Transnational Corporations: The Limits of Direct Corporate Responsibility
To date, multinational corporations have had no direct human rights obligations under international law. Nonetheless, international lawyers can no longer ignore the increasing role of non-state actors in international society. This article suggests analysing existing mechanisms and new proposals for enhancing the accountability of transnational corporations, grouped into those focusing on the responsibility of the home and host states and those centred on the imposition of direct obligations on corporations. This article will specifically draw attention to the limits of some of the suggested normative changes, from a legal-theoretical perspective and in terms of their capacity to address effectively the challenges of the lack of respect for human rights laws.