Materials Science and Engineering A280 (2000) 225 – 228 Effects of heat treatment on compressive properties of AZ91 Mg and SG91A Al foams with open-cell structure Y. Yamada a, *, K. Shimojima a , Y. Sakaguchi a , M. Mabuchi a , M. Nakamura a , T. Asahina a , T. Mukai b , H. Kanahashi c , K. Higashi c a Materials Processing Department, National Industrial Research Institute of Nagoya, Hirate -cho, Kita -ku, Nagoya 462 -8510, Japan b Mechanical Engineering Department, Osaka Municipal Technical Research Institute, Morinomiya, Joto -ku, Osaka 536 -8553, Japan c College of Engineering, Department of Metallurgy and Materials Science, Osaka Prefecture Uniersity, Gakuen -cho, Sakai, Osaka 599 -8531, Japan Abstract Compressive properties were investigated for the as-cast and T6 heat-treated AZ91 Mg and SG91A Al foams with open-cell structure. The foams showed an elastic region at an initial stage, then a plateau region with a nearly constant flow stress to a large strain of about 60%, and finally a densification region where the stress increased rapidly. The relative stress of the as-cast foams was higher than that of the T6 foams, taking into consideration the influence of the relative density. © 2000 Elsevier Science S.A. All rights reserved. Keywords: Metal foam; Mechanical properties; Heat treatment; T6; AZ91; SG91A www.elsevier.com/locate/msea 1. Introduction Metal foams are super-light metals exhibiting unique properties such as high energy absorption [1]. The applications of metal foams are in a wide range of impact energy absorbers, silencers, flame arresters, heaters, heat exchangers, constructional materials, etc. [2]. To date, the mechanical properties of metal foams have been extensively investigated [3 – 9]. These studies have shown that the metal foams exhibit a plateau region with a nearly constant flow stress and that the flow stress in a plateau region strongly depends on the density. Mechanical properties of foams can be related to the mechanics of bending, buckling, plastic collapse and brittle fracture. Gibson and Ashby [1] analyzed the stress – density relation of metal foams from the view- point of plastic collapse. In the present paper, the compressive properties of T6 heat-treated AZ91 Mg and SG91A Al foams with open-cell structure are compared with those of as-cast foams to understand the effects of heat treatment on the mechanical properties of metal foams. 2. Experimental procedure Materials used were an AZ91 Mg (Mg–9wt.%Al– 1wt.%Zn–0.2wt.%Mn) alloy and a SG91A Al (Al– 9wt.%Si – 0.4wt.%Mg – 0.5wt.%Fe – 0.4wt.%Mn) alloy. The AZ91 Mg and SG91A Al foams with open-cell structure were processed by the casting method [10]. A schematic illustration of production of the metal foams is shown in Fig. 1. At first, plaster was poured into a polyurethane foam, and then the plaster mold was heated to 773 K. Because the polyurethane foam was removed during heating, the plaster mold had a porous structure. Each molten metal was poured into the porous plaster mold heated to 873 K. After casting, water was sprayed onto the plaster mold which was broken down by the water spray and AZ91 Mg and SG91A Al foams with open-cell structure were ob- tained. The foams were T6 heat-treated at 688 K for 72 ks for solution treatment and at 443 K for 57.6 ks for aging treatment in AZ91 Mg and at 798 K for 36 ks for solution treatment and at 433 K for 32.4 ks for aging treatment in SG91A Al. Optical micrographs of the polyurethane foam and the AZ91 Mg foam are shown in Fig. 2. It can be seen that the structure of the AZ91 Mg foam was almost the * Corresponding author. Tel.: +81-52-9112111; fax: +81-52- 9166991. E-mail address: yyamada@minim.go.jp (Y. Yamada) 0921-5093/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved. PII:S0921-5093(99)00671-1