Study On Preparation Of Aluminum Foam Sandwich And Mechanical Properties

Referring to light weight, great energy absorption properties of the aluminum foam sandwich (AFS) and excellent performance to improve strength and optimize connection with sandwich structure. Thus, AFS has broad prospects in aerospace, automobile industry, rail transit, precision machine tool, etc. Nowadays, stickiness technology has been used in most of the AFS preparation. However, it will result in low interface bonding strength and easily aging failure in adhesive layer. The Powder metallurgy route can be applied to avoid the shortcomings occurred in the using of AFS. So it will be a development tendency for powder metallurgy preparation method to be used for preparation of aluminum foam sandwich. As the national preparative technique is not mature yet, it is necessary to develop a suitable preparation technology for industrial manufacture.A shorter process of preparation technology for high-performance AFS has been studied in this paper. Pack rolling process for the preparation of expandable prefabricated parts has been given for improving the density of core powder and combination strength between surface layer and core layer. With the purpose to develop a suitable process technology and provide some related theoretical analysis to guide the designing and optimizing of AFS, quasi-static three-point bending behavior and dynamic impact behavior of AFS prepared by powder metallurgy preparation method were investigated comparing with those of samples manufactured with stickiness technology. Comparative analysis can provide some theoretical guide for design and optimization for AFS preparation.Results obtained show that pack rolling process can greatly reduce the wastage rate of powders and increase the interface combination strength. Besides, high powder send density and low defect rate of prefabricated parts have been achieved.Theoretical analysis shows that powder send density is related to the filled amount and reduction rate. When the initial density is higher than2.40g/cm3, the reduction rate ranges from65%to75%, a higher quality prefabricated parts for foaming.Fast and uniformly foaming has been realized by limited foaming in a steel mold. This process can not only reduce energy consumption, but also avoid defects. It means energy saving and avoiding boards melting.An oxidation treatment on TiH2was carried out at450℃for2h, and foaming temperature is700℃, and foaming time lasts90s-120s, the expansion rate is about200%～230%. In the experiment, thickness of AFS is about10mm, with the face board thickness of about lmm, not less than3layers’polygon foams. Average foam dimension ranges from lmm to4mm. Average density of AFS ranges from0.70g/cm3to1.20g/cm3, while the core layer,0.30g/cm3to0.80g/cm3.Three-point bending test of aluminum foam sandwich plate was conducted. The samples were prepared by metallurgical method (YJ-AFS) and adhesive method (NJ-AFS). Typical displacement-loading curves showed that NJ-AFS curve can be divided into two stages including linear elastic stage and instability stage, while YJ-AFS curve existed three stages, which contains linear elastic stage, instability stage and compacting area. Analysis of the failure modes shows that, for NJ-AFS, the failure modes contain mainly core layer fracture and debonding between sheet and core. While for YJ-AFS, two failure modes can be observed. One is collapsed compaction in the core layer, meanwhile, two plastic hinges can be observed. In other instances, shearing happened in the core layer and only one plastic hinge was observed. As it is metallurgical bonding for the interface of YJ-AFS, core layer fracture and debonding shall not happen during bending deflection. The peak load, failure mode and energy absorption of both sandwich plates with different core density and span were compared. The results showed that the peak load rises with increasing core density and decreasing span. However, the span has little influence on the failure mode. The energy absorption of YJ-AFS is influenced by density and deformation pattern. Fracture analysis showed that NJ-AFS and YJ-AFS exhibited brittle fracture, which is shown as smooth cleaves and quasi-cleavage fracture. Debonding failure between sheet and core layer occurs for NJ-AFS. While the interface still bonding closely for YJ-AFS.Dynamic impact measurement results showed that the curve of NJ-AFS can be divided into two stages, initial compression stage (elastic compression stage) and asymptotic failure crush stage. For YJ-AFS, three stages can be observed, which contains linear elastic stage, asymptotic compression stage and asymptotic failure crush stage.For NJ-AFS, the failure modes are mainly shown as shearing impact mode and brittle failure impact mode. While three modes, which are steady-state impact mode, caving impact mode and brittle impact mode can be observed for YJ-AFS. Moreover, the mode I exhibits wider Plateau area and longer buffer time. Kinetic energy control experiment shows that the damage of sample tends to serious with increasing energy. The results show that only YJ-AFS has great cushion effect under steady-state impact mode and caving impact mode, especially when the input energy reach50J and70J, cushion time of YJ-AFS is twice as much as that of NJ-AFS. Mixed fracture was observed at both fracture surfaces (NJ-AFS and YJ-AFS) under impact deformation. No large, collective and smooth flake grain appeared at the whole surface, as grains are crushed under impact effect. Besides, the slip steps can be observed at the fracture surface of sheet as well as bending occurred obviously. At the interface of NJ-AFS, wide and deep cracks appeared. However, the bonding of the interface of YJ-AFS is in a good condition.