Papers by Keyword: Weldability of Magnesium Alloys

Abstract: Magnesium alloys are a part of a group of lightweight and ultra-lightweight alloys, which are important in practical use in constructions. QE22 casting magnesium alloy containing silver, rare earth elements and zirconium is characterized by creep resistance up to the temperature of 200 °C, while during a short exposure it can resist up to the temperature of 250°C. Nowadays, QE22 magnesium alloy are used for casting into sand moulds. In castings of magnesium alloys defects or inconsistencies (such as casting misruns, porosities and cracks) often appear, particularly in huge dimensional castings. Such defects are repaired with the use of padding and welding. Welded joints must ensure suitable operational properties, mainly in terms of creep, so that the repaired casting can work under the same conditions as the correct cast. The basic source of information about the cause and cracking propagation is fracture after creep test. The quantitative fractography, in particular profilomety, allows to describe the fracture and basis on it conclude the causes of destruction. In this paper quantitative procedure for assessing the fracture profile of QE22 welded joints after creep test was worked out. Base on its analysis result, it was found that creep resistant of the QE22 joints is determined by eutectic areas, therefore they must be heat treated after welding joints.

Abstract: This work, in combination with industrial tests of casting welding, shows that the causes of high-temperature brittleness are the partial tears of the structure and the hot cracks of both the castings, as well as the welded and padded joints. Such phenomena should be treated as irreversible failures caused by the process of crystallization that is in the area of co-existence of the solid and liquid structural constituent. Nil-strength temperature (NST), nil-ductility temperature (NDT) and ductility recovery temperature (DRT) were determined using Gleeble 3800. Obtained results enabled the defining of brittle temperature range of MSR-B magnesium alloy. The assessment of the resistance to hot fractures was conducted on the basis of the transvarestriant trial. The transvarestriant trial involves changing of strain during welding. It was stated that the range of the high-temperature brittleness is very broad, which significantly limits the application of the welding techniques to join or repair elements made of the MSRB alloy. brittleness is caused mainly by metallurgical factors, i.e. precipitation of intermetallic phases from the solid solution.