High strength aluminium alloy AA7075 (AleZneMgeCu) is a precipitate hardenable alloy widely used in the aerospace, defense, marine and automobile industries. Use of the heat treatable aluminium alloys in all these sectors is ever-increasing owing to their excellent strength-toweight ratio and reasonably good corrosion resistance. The shortage in corrosion resistance, however, usually poses negative concern about their reliability and lifetime when they service in the variable marine environments. These alloys also exhibit low weldability due to poor solidification microstructure, porosity in fusion zone and lose their mechanical properties when they are welded by fusion welding techniques. Friction stir welding (FSW) is a reliable technique to retain the properties of the alloy as the joining takes place in the solid state. The welds are susceptible to corrosion due to the microstructural changes in the weld nugget during FSW. In this work, the effect of post weld treatments, viz., peak aging (T6) and retrogression & reaging (RRA), on the microstructure, mechanical properties and pitting corrosion has been studied. Friction stir welding of 8 mm-thick AA7075 alloy was carried out. The microstructural changes of base metal and nugget zone of friction stir welds were studied using optical microscopy, scanning electron microscopy and transmission electron microscopy. Tensile and hardness test of base metal and welds has been carried out. Pitting corrosion resistance was determined through dynamic polarization test.It was observed that the hardness and strength of weld were observed to be comparatively high in peak aged (T6) condition but the welds showed poor corrosion resistance. The resistance to pitting corrosion was improved and the mechanical properties were maintained by RRA treatment. The resistance to pitting corrosion was improved in RRA condition with the minimum loss of weld strength.
Annular sub-mitral aneurysms are rare lesions of varied etiology. A sub-mitral membranous curtain may be a potential area of weakness through which these lesions expand. Initially described in young males of African origin and reported from varying geographical areas, these lesions arise from the atrioventricular groove in close relation to the mural leaflet. They may cause pressure effects, lead to mitral incompetence and left ventricular dysfunction. Key issues during repair are proximity to the circumflex coronary artery, atrioventricular junction and progressive involvement of the mitral valve. This case report of a calcified bi-lobed sub-mitral aneurysm with communication to the left atrium discusses the anatomical basis of the lesion, the role of computed tomogram angiography in pre-operative evaluation and surgical management.
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