INCLUSIONS IN PERMANENT MOLD CAST MAGNESIUM
This research is part of an ongoing effort to increase the use of magnesium alloys to a signifi cant level in the aerospace and automotive industries and to reduce vehicle weight, fuel consumption, and emission of harmful gases.
M
protective atmospheres such as sulfur hexafl uoride (SF6), reaction products of MgO and MgF2 can become entrapped in the melt. In addition, melt turbulence during melting,
which they arise. Inclusions can arise from reactions with air where magnesium reacts with oxygen to form MgO, reactions with fl uxes entrapping fl ux components (e.g., MgCl2
, CaCl2 ) and fl ux reactions with oxygen to form MgO. Even with the use of
handling, and pouring can be a source of inclusions in magnesium castings. A wide variety of inclusion assessment techniques are available for magnesium
28 | METAL CASTING DESIGN & PURCHASING | Mar/Apr 2017
ABDALLAH ELSAYED, RYERSON UNIVERSITY (TORONTO) CURRENTLY AT NEMAK CANADA CORPORATION (WINDSOR, CANADA); COMONDORE RAVINDRAN AND ELI VANDERSLUIS, RYERSON UNIVERSITY (TORONTO); SOPHIE LUN SIN, RYERSON UNIVERSITY (TORONTO) CURRENTLY AT INRS (QUEBEC CITY, CANADA).
agnesium alloys have been gaining consideration as possible alternatives to aluminum alloys to reduce vehicle weight in aerospace and automo- tive applications. Magnesium alloys are about 35% lighter than aluminum alloys. However, only 0.3% of the total automotive vehicular weight in North America is composed of magnesium alloys, while 8.3% is composed of aluminum alloys. In terms of total weight, each passenger car contains only 11.02 lbs. (5 kg) of magnesium, yet 264.5-308.6 lbs. (120–140 kg) of aluminum.
T e widespread use of magnesium alloys for aerospace and automotive applica-
tions is hindered by their high reactivity, which increases the probability of inclusion formation during casting processes. Inclusions in magnesium alloys compromise corrosion resistance, increase porosity, produce unfavorable surface fi nishes, and reduce mechanical properties, in particular ultimate tensile strength and elonga- tion. Two major types of inclusions in magnesium alloys occur: intermetallic and non-intermetallic. Intermetallic inclusions are almost always iron-rich phases, while non–intermetallic inclusions include sulfi des, fl uorides, sulfates, chlorides, nitrides, and oxides, with oxides being the most dominant. Avoiding inclusions in magnesium alloys is diffi cult due to the many sources from
and its alloys. T ese techniques vary from simple observational methods, such as metallographic and fracture bar examinations, to highly sophisticated online methods, such as liquid metal cleanliness analyzers. Since no industry standard for examining inclusions in magnesium alloys exists, the techniques employed are foundry-dependent, which complicates comparisons be- tween facilities. T is article aimed to characterize and examine the eff ects in ZE41A and AZ91D magnesium alloys and their infl uence on microstructure and mechanical properties. By better understanding and documenting metal handling, the resulting scrap reduc- tion, casting quality enhancement, and associated cost reductions will improve foundry competitiveness. T is research is part of an ongoing eff ort to increase the use of magnesium alloys to a signifi cant level in the aerospace and automotive industries and to reduce vehicle weight, fuel consumption, and emission of harmful gases. T e general procedure was the
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