Bruno Bourassa, Danny
Jean, Alain Lemieux, Joseph Langlais and Fred Major, Rio Tinto Alcan, Jonquiere, Can- ada, conducted a study ex- amining how the interrelated topics of homogenization time and temperature, iron level and cooling rate af- fected mechanical properties and phase transformation in 6061 and 6082 wrought alloys. Once they had their results, they looked at ways to improve the casting of 6061 aluminum. Conclusions • Aluminum wrought alloys in the 6000 series can be cast to shape if the chemistry and casting process are op- timized to control hot tearing.
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6082 tended to degrade with an increased iron level.
• Composition and alloy treat- ment with grain refiners and strontium can limit hot tearing in alloys like 6061.
Shown are the fully machined test plates used in Robert Tuttle’s examination of the accuracy of ultrasonic testing. Detected defects are outlined in pink.
• 6082 alloy showed a more rapid deterioration in ductility with slower cooling rates than did 6061.
• 6061 alloy was controlled more eas- ily via microstructure and exhibited high mechanical properties, particu- larly through heat treating.
• Six hours at 1,058F (570C) suffi- ciently converted the microstruc- ture of 6061 alloy when cast to shape. 6082 alloy benefitted from a homogenizing treatment of 12 hours. Beyond 12 hours, both al- loys deteriorated.
• Iron levels from 0.1-0.15% were equally effective in the 6061 alloy;
• The casting process used with these alloys can have an effect on the properties achievable, but no process was singled out as best.
Ultrasonic Testing Comes Out on Top
According to Robert Tuttle, Sagi-
naw Valley State Univ., Saginaw, Mich., many steel casting facilities have expressed concern about the reliability of ultrasonic testing of castings with heavy section thick- nesses. Typically, these metalcasters conduct x-ray testing without the same concerns. In “A Gage R&R Study of the ASTM
A609 Ultrasonic Testing Standard,” Tuttle examined the variances he could find among different operators using the test. Would it prove to be less re- peatable than x-ray testing? In the study, five plates were cast
with varying levels of shrinkage de- fects. The plates were then x-rayed and ultrasonically tested by five different metalcasting facilities. Conclusions • X-ray ratings showed a dramatic variation between metalcasting facilities.
• X-ray operators could not agree on the ratings, and statistical analysis of the x-ray results found the operator to be a significant contributor to the variation in ratings. In the worst case scenario, 62% of radiographers disagreed with the most commonly issued rating.
• Results from the ultrasonic testing resulted in little disagreement. No statistically significant effect on the ultrasonic rating was found based on the operator making the reading.
• A method was developed that could successfully predict the ultrasonic rating of a casting using solidifica- tion modeling.
METAL 44 Metal Casting Design anD PurChasing May/June 2011
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