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ASTM International has accepted a new aluminum permanent mold separately cast test bar developed through an AFS Research Project as an alternative methodology applicable to the ASTM B108 standard. The new mold configuration, called the “Case mold,” has been accepted as an alternative approved design.
The AFS research project originated within its Aluminum Division in 2009, with the initial objective of developing and confirming best practices for casting A356 alloy with highest, or optimum, mechanical properties. Separately cast permanent mold test bars were chosen as the means to evaluate the mechanical properties. However, the standard test bar mold, the “Stahl mold,” which underpins the ASTM B108 standard, suffers from microporosity in normal application and does not always yield best mechanical properties. Based on a successful experience using a step-mold for magnesium, researchers at Case Western Reserve University undertook a computer simulation study to investigate whether a knife-ingate into the gage section of the “Stahl mold” design could theoretically reduce microporosity. Comparative results with the standard ASTM B108 mold confirmed the micro-porosity could be reduced from a simulated 3% to as little as 1%.
Based on the computer simulation results, researchers designed the “Case mold” with a thin knife-ingate into the best bar gage section. Separately-cast test bars using the Stahl and Case molds were poured in both A356 and 319 alloys at Case Western Reserve and at two commercial metalcasting facilities. The test bars were treated to the T6 condition. The 319 alloy was also treated to the T7 condition. In all instances, the test bars consistently showed a measurable increase in mechanical properties with the Case mold versus the Stahl Mold.
One of the key advantages of the new Case mold test bar is the “sweet spot” for optimal mechanical properties is achieved at a mold temperature 600-625F, which is readily and easily achieved in metalcasting floor practice. Embedded heaters and thermocouple connections in the new Case mold design also facilitate foundry-floor capability for pouring repeatable test bars.
Separately-cast test bar properties are not necessarily fully representative of the actual properties attained in an actual casting. The solidification conditions and microstructural characteristics must be similar in both the test bar and the casting.
Foundries now can manufacture the Case mold design as depicted in the new ASTM standard. It is also available commercially.
壓鑄展-鑄造展-2016第十七屆廣州國(guó)際壓鑄、鑄造及工業(yè)爐展覽會(huì)-中國(guó)最受關(guān)注的壓鑄鑄造展會(huì)-巨浪展覽
-The 17th Guanzhou
Die-casting,Foundry&Industry Furnace Exhibition
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