Uncontrolled high frequency current causes cracking in the heat-affected zone of aluminum alloy 6061 weldments during tungsten inert gas ac welding. Cracking developed when an improperly adjusted superimposed high frequency current was agitating the semimolten metal in the areas of grain boundary

Fish, R. E.

English

NASA Technical Reports Server

October 1968	 Brief 68-10383 
NASA TECH BRIEF . 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Effects of High Frequency Current in Welding Aluminum Alloy 6061 
Cracking has been found to occur frequently in 
the heat-affected zone of aluminum alloy 6061 weld-
ments during TIG (tungsten inert gas) ac weld-
ing. The cracks appeared to be intergranular 
separations, normal to overheated aluminum alloy. 
An ensuing investigation showed the cracks to 
be superficial surface defects, located only on the 
torch side of the weld in areas of grain boundary 
melting and seldom more than 0.015 inch deep. The 
cracking continued to occur even when the best 
known TIG welding procedures were employed and 
strict control was maintained. 
Continuous observation during welding revealed 
that the cracks developed when improperly adjusted, 
or erratic, superimposed high frequency current was 
agitating the semimolten metal in the areas of grain 
boundary. Lack of, or depletion of, boundary con-
stituents combined with rapid freezing and normal 
shrinkage stresses (hot shortness) resulted in boun-
dary voids or cracks. 
A series of original tests was performed, which 
involved the heating of test plates to temperatures 
normal to the heat-affected zone and applying only 
high frequency current. The high frequency arc was 
varied by controlling arc length, electrode diameter, 
and the welding power supply for phase shift and in-
tensity. Each plate was examined for surface defects 
immediately after testing and after 30 days.
An increase in the magnitude of any variable re-
sulted in an increase in arc length or plate tempera-
ture and caused the most noticeable effect. After 
natural aging, severe crack propagation was found 
in areas exhibiting moderate boundary melting or a 
dendritic freezing pattern. The results were consid-
ered conclusive in demonstrating that uncontrolled 
high frequency current alone was extremely dele-
tefious to the finished weld. 
Samples sectioned from actual parts containing 
the defects were subjected to static tension, fatigue, 
and salt spray corrosion tests. In all samples, the 
defects, if not removed in accordance with recom-
mended procedures, had deleterious effects. 
Note: 
Inquiries concerning the test procedures and 
results may be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: B68-10383 
Patent status: 
No patent action is contemplated by NASA. 
Source: Robert E. Fish 
of North American Rockwell Corporation 
under contract to 
Marshall Space Flight Center 
(MFS-18337) 
Category 05 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States	 will be free from privately owned rights.
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Effects of high frequency current in welding aluminum alloy 6061

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