Abstract
We investigated pore formation in aluminum foams by controlling primary crystal morphology using three master alloys. The first one was a direct chill cast A2024 (Al-Cu-Mg) alloy (DC-cast alloy). The others were A2024 alloys prepared to possess fine spherical primary crystals. The second alloy was made by applying compressive strain through a Strain-Induced Melt-Activated process alloy (SIMA alloy). The third one was a slope-cast A2024 alloy (slope-cast alloy). Each alloy was heated to either 635 °C (fraction of solid fs = 20%) or 630 °C (fs = 40%). TiH2 powder was added to the alloys as a foaming agent upon heating them to a semi-solid state and they were stirred while being held in the furnace. Subsequently, A2024 alloy foams were obtained via water-cooling. The primary crystals of the DC-cast alloy were coarse and irregular before foaming. After foaming, the size of the primary crystals remained irregular, but also became spherical. The SIMA and slope-cast alloys possessed fine spherical primary crystals before and after foaming. In addition to average-sized pores (macro-pores), small pores were observed inside the cell walls (micro-pores) of each alloy. The formation of macro-pores did not depend on the formation of the primary crystals. Only in the DC-cast alloy did fine micro-pores exist within the primary crystals. The number of micro-pores in the SIMA and slope-cast alloys was one third of that in the DC-cast alloy.
Highlights
New, lighter materials are required to reduce the environmental impact and cost of transportation equipment, including automobiles and aircrafts [1,2]
Fukui et al [4,5] improved the compressive properties of aluminum foam using the super duralumin A2024 (Al-Cu-Mg) alloy, which is a well-known high-strength and lightweight material, as a base metal to improve the strength of the foam
The objective of this study is to investigate the effects of the large primary crystals present inside the melt on pore formation in aluminum alloy foams in a semi-solid state
Summary
Lighter materials are required to reduce the environmental impact and cost of transportation equipment, including automobiles and aircrafts [1,2]. Aluminum foam has attracted significant attention in recent years for meeting weight reduction and safety requirements. Aluminum foam has many pores and, owing to its ultralight and excellent shock-absorbing properties, could be applied to transportation equipment. The compressive properties of aluminum foam must be improved before it can be effectively used for this purpose. The compressive properties of foams are determined by their base metal and structure [3]. To this end, Fukui et al [4,5] improved the compressive properties of aluminum foam using the super duralumin A2024 (Al-Cu-Mg) alloy, which is a well-known high-strength and lightweight material, as a base metal to improve the strength of the foam
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