castings. When best elongation and highest strength are de- sired, one must control the shape of the silicon phase. This was shown most clearly in a study of quality in aerospace A357 alloy castings.24


It was found that the Quality Index was well represented by the equation: Equation 12


where Q is the quality index (in MPa), N is the cell count (alu- minum cells per 0.0001 square inches), AR is the average aspect


Control of the silicon phase may be accomplished by rapid solidification, by heat treatment, and/or by small additions of Na or Sr, which ‘modify’ the morphology of the silicon in the eutectic phase. Modification is a fascinating, complex subject; one that is extremely important for best quality in Al-Si casting alloys. It will not be considered here, however, since it has been reviewed elsewhere.25


ratio of the silicon particles, and P is the area percent of porosity found on the polished surface of test specimens. The magnitude of the coefficient of the third term (1100 MPa) shows the im- portance of silicon particle shape (AR) on casting quality.


Diameter of Initiating Pore (µm)


Figure 13. Measured fatigue life of W319 alloy at alternating stress of 96.5 MPa.22


Cooling Rate, ºC/s Figure 14. Volume fraction porosity in Al-7Si-0.3Mg (A356) alloy castings.7 16 International Journal of Metalcasting/Winter 11


Hydrogen Content, cc/100 gm


Pore Volume Fraction, %


Cycles to Failure


Pore Volume Fraction, %


Cycles to Failure


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87