Structural foams or integral foams are components with a dense skin and a cellular core. Thermoplastic integral foams are manufactured in extrusion processes and are established in industry since approximately five decades. The situation of metal foams is completely different. So far, similar approaches to produce metal integral foams are rare. We produce integral foams out of conventional magnesium alloys (AZ91, AM60). The new process was developed at the WTM-Institute in Erlangen, Germany. The parts can be produced with a magnesium injection moulding machine or a metal die casting machine. A chemical blowing agent, which releases gas at an elevated temperature, is mixed into the melt in the die. The melt solidifies to a dense skin because of the fast heat dissipation at the die walls whereas a foam core is formed inside the casting. There is a continuous density transition between the compact face sheet and the foamed core which is characteristic for an integral foam. The integral foams offer lower density, increased energy absorption capacity, increased specific bending stiffness and improved damping capacity compared to compact castings of the same thickness.
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