Trans-Varestraint試験法による溶接金属の凝固割れ感受性の研究(2)

Abstract

In fusion welding of structural aluminum alloy plates solidification cracking frequently occurs in the weld metal and gives rise to serious problems for the soundness of the welded joint.In this report, using the Trans-Varestraint test which was developed previously, authors have investigated the sloidification crack susceptivility of commercially used structural aluminum alloy plates.Firstly the time required for straining in the specimens given by various bending blocks and the time required for the propagation of solidification crack during straining were dynamically investigated. using 6.1mm thick 5083 aluminum alloy plates. Secondly the properties of the ductility whithin the solidification brittleness range were measured and also evaluated for eleven commercial aluminum alloys.The main conclusions obtained are as follows:(1) In the observation with high speed cine camera the propagation of the solidification crack which occurs during the Trans-Varestraint test was so fast that the time required for the completion of a crack was from 0.005 to 0.02 sec in the case of 2.1% augmented-strain for a 6.1mm thick 5083 aluminum alloy plate.Moreover a crack started in the vicinity of the trailing end of the puddle and propagated rearward of the puddle along the weld bead.(2) Indices of crack susceptibility such as the brittleness temperature range (BTR), the minimum augmented-strain required to cause cracking (emin) and the critical strain rate for temperature drop (CST) were decided for these aluminum alloys. Thus, in order of the CST value these alloys are placed in this experiment as 1070. 3003, (7075, 5154, 5052, 2024), (6061, 2017, 74S, 5052) and 5083.(3) The BTR for each alloy is roughly proportional to the nominal solidification temperature range between liquidus and solidus, although there is a considerable scatter. Moreover the CST value for each alloy can be approximately represented by the εmin/BTR.