THE INFLUENCE OF HEAT TREATMENT ON PROPERTIES OF THREE-METAL EXPLOSION JOINT: AlMg-Al-Steel

Aluminium and its alloys are commonly used in shipbuilding structures applications as include main strength members such as hulls, deckhouses and other applications as stack enclosures, hatch covers, windows, air ports, accommodation ladders, gangways, bulkheads, deck plates, ventilation equipment, lifesaving equipment, furniture, hardware, fuel tanks and bright trim. Separately interesting is application of aluminum alloy with magnesium (series 5 000). This alloy has good weldability and high mechanical properties at low temperatures as well as high corrosion resistance in seawater. Because of compromise between design requirements regarding on materials properties as well as on ships weight, the ship-carrying part are worked out off structural steel and upper side from aluminium alloy. Explosion welding is, as solid cold joining process, in shipbuilding mostly used at working out of transition Al-Steel joints because of intention to avoid brittle intermetalic compounds by melting welding process. This is a process in which coalescence is effect of high-velocity movement together of the parts which be joined produced by a controlled detonation. Even though the fact that the heat is not applied in making an explosion weld, it appears that the metal at the interface is molten during welding. This heat comes from several sources, from the shock wave associated with impact and from the energy expanded in collision. Heat is also realised by plastic deformation associated with jetting and ripples formation at the interface between the welded parts. When a cladding plate collides with a base plate, a formed jet cleans the surface of plates. Due to unstable plastic flow of metal in the surrounding of the point of incipient flow a wavy interface is formed which is characteristic for the explosive welded metals. It is founded necessity off metal flow plastically in order to provide a quality weld. Analysis of the explosive metal welding phenomenon confirms that welding is directly consequence of the high speed of collision. Experiments confirm that there are critical values for optimum collision. This set of parameters and its interaction makes so-called “the welding window”, whereby the critical parameters are: – collision velocity Vc. – collision angle required for the appearance of jetting. Relations between those parameters are graphically present in Figure1 1 . Curve a a’ in Figure 1 represents the critical collision angle required for the appearance of jetting. Line b b’ represents the upper velocity limit Vc, which is in the range of 1,2 1,5 the sound velocity of clad material. Values of starting angle are, within the range of 3-18°, are represented by lines C C’ and D -