24. Savitzky, A. and Golay M., “Smoothing and Differentiation of Data by Simplified Least Squares Procedures,” Analytical Chemistry, vol. 36, no 8, pp. 1627-1639 (1964).
25. MacKay, R., M. Djurdjevic, M. and Sokolowski, J.H., “The Effect of Cooling Rate on Fraction Solid of Metallurgical Reactions in 319 Alloy,” AFS Transactions, vol. 108, pp. 521-530 (2000).
26. Dixon, W. J. and Mood, A.M. “A Method for Obtaining and Analyzing Sensitivity Data.” Journal of the American Statistical Association, vol. 43, issue 241, pp. 109-126 (1948).
27. Kasprzak, M., Kasprzak W., Kierkus, W.T. and Sokolowski J.H., “A Novel Solution Treatment during Solidification for Al Based Alloys,” International Conference at the University of Birmingham, UK (invited paper) (April 23, 2002).
28. Wang, Q.G., Apelian D., Lados D.A., “Fatigue Behaviour of A356-T6 Aluminum Cast Alloys, Part I Effect of Casting Defects,” Journal of Light Metals, vol. 1, no. 1, pp. 73-84 (2001).
Technical Review and Discussion:
Comparison Between Wedge Test Castings and Component Engine Block Casting Properties R. L. Mackay, Nemak of Canada Corporation, Windsor, Ontario, Canada
J. H. Sokolowski, University of Windsor, Windsor, Ontario, Canada
Reviewer: There is a lot of detail on relating to the specific gravity to hydrogen levels that does not fit the main focus of the paper. The authors could simply point out that standard degassing was conducted to a 2.70 level.
Authors: Indicating simply that degassing was preformed so that a RPT density of 2.70 grams/cc does not provide a com- plete picture on hydrogen concentrations, as a reduction in RPT test sample density could be due to both elevated oxide concentrations and dissolved hydrogen in the melt. During interdendritic feeding both dissolved hydrogen and oxides will have somewhat different effects on pore nucleation and pore growth. The focus on the manuscript was the effect of composition on porosity formation on a progressively solidi- fied wedge casting. Hydrogen itself will not nucleate pores as oxides will, however, the degree of porosity, its size and distribution, can be due to the level of dissolved hydrogen.
While the authors are aware that the RPT method is used in some manuscripts, there can be shortfalls as mentioned above. Using the Alspek unit in conjunction with the RPT could provide better clarity as to the controlling factors gov- erning pore nucleation and growth and to better provide a technical discussion on the interpretation of the manuscripts results. True, no assessment was made about the concen-
tration of oxides in the melt and one may consider this an omission in the above argument. However, the furnace used to prepare the melts is not only degassed with Argon, but a protective Nitrogen blank is used to preserve melt qual- ity. In addition a filter is used in the rigging setup for the wedge casting. Both aspects of the casting methodology should qualitatively keep oxide concentrations in the solidi- fied wedge casting extremely low.
Reviewer: There is inconsistency in identification of loca- tion of fatigue bars. The paper shows distances from 70- 12mm with a significant variation in microstructure. Why were the samples not taken from the same location?
Authors: The problem here is that with the low variation in porosity of this range of SDAS where fatigue test samples are extracted (.010%), coupled with the low number of test samples, it was not possible to use the wedge casting to clear- ly define a fatigue life ranking for the alloys studied. More wedge castings could not be made to support a larger testing population. Due to the progressive solidification conditions, porosity variation would be low and thus a defined ranking was difficult to do. It is explained in the manuscript that the approach taken was not as successful as hoped.
This however does not negate adding this information in the manuscript, as many researchers have attempted to draw conclusions from using a small number of fatigue test samples in progressively solidified castings. Secondly, and as addressed in the manuscript, the difference in fatigue performance became evident between the W319 and U328 alloys at the beginning of the staircase. This illustrates the importance of fatigue performance differences with alloys and the solidification environments.
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International Journal of Metalcasting/Fall 10
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