Study on MIG Spot Welding of Aluminum Alloys (Report 1)
Cracking in MIG Spot Weldments and its Prevention by Utilizing Pressurized Arc Atmosphere
1977 Volume 46 Issue 2 Pages 96-103
Details
1977 Volume 46 Issue 2 Pages 96-103
In MIG spot welding of aluminum alloys one of the the most important problems to be throughly solved is establishment of countermeasures for the high sensitivity to circular cracking in the weldments. The authors studied to clarify the cracking mechanism and to get the preventive measure for the cracking through rising the ambient pressure. The conclusions are summarized as follows:
(1) Circular cracks are intergranular hot cracks occurring in the locations wherein solidification has been delayed to the last on account of formation of finger-type fusion zone pattern and of poor heat transfer through the interface of the two welding sheets.
(2) Circular cracks are classified as the following three types: (i) overlap crack, (ii) HAZ crack, (iii) notch crack or peripheral crack at the interface.
(3) By simply but firmly pressing the nozzle of a MIG welding torch towards the surface of welding sheet without resorting to provision with any special pressure controlling chamber, pressurized arc atmosphere for MIG spot welding can be obtained.
(4) With increase in ambient pressure the fusion zone contour of weldment changes from finger-to bell-type. In accordance with this change weld cracking tends to decrease. Especially noteworthy is that overlap cracking and HAZ cracking can be wholly prevented in the ambient pressure over 3 atm's. Notch cracking is generally hard to shut out its appearance completely, however, the crack size can be minimized to micro scale.
(5) Welding at higher ambient pressure brings about no change in specific wire melting rate per ampere-second in case of lower wire feed rate of 100mm/s. At higher feed rate of 165mm/s and 215mm/s, however, higher ambient pressure gives rise to increase specific melting rate. This result contradicts the experimental data given by Salter and Nishiguchi et al.. With respect to this discrepancy short discussion is given.
