significant amounts of pearlite and fer- rite in all the conditions tested. Ferrite increased with decreased austenitiza- tion temperature and increased section thickness. Tensile properties in the 0.6 in. (1.6 cm) step blocks were higher than those seen at other thicknesses. Te coarser as-cast structure obtained in thicker sections gives some deterio- ration in properties, but austemperabil- ity limits in the samples also contrib- uted to these differences.


Conclusions Step block castings of IADI were


produced with thicknesses of 0.6 in. (1.6 cm), 1 in. (2.5 cm) and 2 in. (5.1 cm). Two alloys were considered, a ‘low alloy’ composition with manganese concentrations of 0.4wt% and copper concentrations of 0.7wt% and a ‘high alloy’ composition with manganese concentrations of about 0.4wt%, copper concentrations of 0.7wt% and nickel concentrations of 0.7wt%. Te low alloy samples were austenitized for four hours at 1,472F (800C) and 1,499F (815C). Te high alloy samples were austenitized for four hours at 1,459F (793C) and 1,477F (803C). Austem- pering was performed on all samples at 698F (370C) for four hours. Te 0.6 in. (1.6 cm) thickness sec-


tions received the hardest quench and no pearlite was detected in any of the conditions tested at this thickness. As expected, the ferrite content decreased with increased intercritical austenitiza- tion temperature. At a section thick- ness of 1 in. (2.5 cm), no pearlite was found in the high alloy conditions while a small amount of pearlite was found in the two low alloy conditions. At a section thickness of 2 in. (5.1 cm), significant amounts of pearlite and fer- rite were in all the conditions tested and the ferrite concentration was about the same for all four conditions. Te pearlite amount increased with increased austen- itization temperature for both the low and high alloy conditions. Te percent ferrite increased and the ausferrite con- tent decreased with section thickness. Te changes were larger in both alloys at the higher austenitization temperatures. For all four conditions, the hardness was highest in the 0.625 in. (1.6 cm)


56 | MODERN CASTING May 2014


section thickness samples. As expected, for most conditions, the hardness increased with higher austenitization temperatures and subsequent lower intercritical ferrite concentrations. Hardness also decreased with increased section size and ferrite concentrations. Te tensile properties in the 0.6 in. (1.6 cm) step blocks were higher than those seen at other thicknesses. Yield and tensile strengths were higher and in almost all cases, elongation was also increased. Te coarser as-cast structure obtained in thicker sections gives some deterioration in properties, but austem- perability limits in the samples are also contributing to these differences.


Presentation Effect of Vacuum Assisted Filling


and Solidification Under Pressure of A356, A206, Modified 319 and 535 Aluminum Alloys on Tensile Proper- ties Using the Lost Foam Casting Process (14-071)


Authors H. E. Littleton, J.A. Griffin and R.D.


Foley, University of Alabama at Bir- mingham (UAB)


Background Previous research by the Lost Foam


Consortium demonstrated a significant


improvement in tensile elongation and a reduction in porosity of samples, sectioned from an engine block cast- ing poured at low temperatures and a vacuum of -4.5 psig on A319 and A356 aluminum alloys. Additionally, in prior research, solidification under 150 psig (1.03 MPa) pressure also reduced porosity and increased tensile elonga- tion. Tis paper describes the casting procedures used and combined effect of vacuum assisted pouring (VAP) and solidification under pressure (SUP) on tensile properties of A356, A206, 319m and 535 aluminum alloys. Ultimate tensile strength and elongation were further increased with this combined casting procedure.


Conclusions Tis study demonstrated that A356,


A206, 535 and 319m aluminum alloys can be successfully poured at 110F (43C) above liquidus temperatures using the vacuum assisted pouring process. Tis pouring temperature is significantly less than typical temperatures used in lost foam casting facilities. Tis results in significant energy savings and extends melting and holding furnace life. Te Al-Si alloys (A356 and 319m)


showed some, but not dramatic improvement in tensile properties with VAP/SUP, even when fracture


This illustration shows the lost foam metal filling model. Metal fill rate and pyrolysis removal rate can be increased by increasing the pressure differential between the metal and sand.


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