This page contains a Flash digital edition of a book.
• 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.


• X-ray operators could not agree on the ratings, and statistical analy- sis of the x-ray results found the operator to be a significant con- tributor to the variation in ratings. In the worst case scenario, 62% of radiographers disagreed with the most commonly issued rating.


• A method was developed that could successfully predict the ultrasonic rating of a casting using solidifica- tion modeling.


Demystifying Magnesium Casting Wouldn’t it be nice to know, once


and for all, which emerging method of casting magnesium alloy AZ91 is and will be the best, and which will be doomed to 8-track-like obscurity? Liang Wang, Ratessiea Lett, Ser-


gio Felicelli and John Berry of Mis- sissippi State Univ., Mississippi State, Miss., set out to examine four differ- ent processes: indirect squeeze, low pressure permanent mold (LPPM), T-Mag (a permanent mold casting process involving filling from the bottom) and ablation (a sand casting


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.


process in which the mold is blasted away with water during solidifica- tion). Magnesium automotive control arms were cast in all four processes at several different metalcasting facilities, and the parts were evaluated through microstructure characteriza- tion, mechanical testing and scan- ning electron microscope analysis of fracture surfaces.


Conclusions • The T-Mag and ablation processes produced the best castings according to defect and fracture surface analysis. • According to an analysis of four-point


• Castings made in the ablation pro- cess presented higher ductility than the other processes. None of the ablation samples could be broken through four-point bending testing.


bending testing, T-Mag castings exhibited better mechanical properties than squeeze cast and LPPM parts.


• Squeeze casting produced fine den- drites, T-Mag yielded the largest average grain size, and LPPM and ablation produced similar grain size distributions.


• Significant amounts of shrinkage porosity and oxide film defects were found in the squeeze cast and LPPM samples.


When Rare Makes It Well Done


What happens when you use rare elements (cerium and lanthanum) to modify a ubiquitous alloy (A356)? In “Effects of Rare Earths on the


As-Cast Microstructure of an Al-Si-Mg Alloy,” Adel Mohamed, Agnes Samuel and Fawzy Samuel of the Universite du Quebec a Chicoutimi, Chicoutimi, Canada, and Abdulrahman Al-Ahmari, King Saud Univ., Riyadh, Saudi Arabia, examined the effects of the elements. Tey addressed the solidification process through thermal analysis, measured microstructure with conventional optical microscopy and electron probe micro- analysis, and examined eutectic silicon particle characteristics through quantita- tive image analysis.


Visible here are casting defects on the fracture surfaces of four-point bending test specimens taken from control arms produced by (clockwise from top left) squeeze casting, low pressure permanent mold casting, ablation and T-Mag casting.


52 | MODERN CASTING May 2011


Conclusions • The characteristics of the eutectic arrest were significantly modified


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