Pumice stone added syntactic foam metal production, physical and mechanical properties analysis

As manufacturing technology develops in metal marketing, manufacturers are being pushed to create unique products in order to be lead in their market. Hybrid products are being popular and preferrable because of pure metals are able to serve to a certain extend in terms of mechanical properties. Beside of that rather than strength of material having light based pieces are being important in certain systems. Light based products are mostly preferred by construction dependent structurals and vehicles which are exposed to weight regulation by government to classify them according to tax payment. In addition, the system which should meet energy absorption requirements designers and manufacturers tends to prefer single or simple pieces instead of complex systems in order to meet absorption energy demands. It is familiar for most that aqueous, polymers and glass foam products are available in daily life. Although it was difficult to form it because of high temperature and reactivity of molten metal was required, with a latest technology and improvement those disadvantages were overcame. New type of product which is called as "Foam Metal" meets with that requirements and serves to metal industry as an alternative product. Foam metal consists of internal hollow structrures inside of itself which helps to reduce used material weight in unit volume. This provides cost reduction in final product in aspect of the least weight the least cost. Internal hollow spaces absorps energy which occurs during shock loading. This is an attractive feature especially for automative industry to have feasible safety and crash system. Not only for safety but also for isolation systems metal foam is an attractive material. Because of its internal space, it improves noise and heat transfer in order to protect design target. Other interest area for foam metal is mainly in medical, architecture, aerospace industry and other industrial fields. There are many different manufacturing techniques and different foam metal classification are available for foam metals. Not only hollow type but also matrice material can be different and derrivable depending on needs and applied application area. Hollow metal spheres, water-soluble salts, carbon-based structures (cenosphere) or glassy spheres containing micro voids are commonly used and tried to form voids together with molten metal during foam metal production. Also aluminum, magnesium, copper, iron based metal and their alloys can be used to form foam metal. Different production techniqu has been studied on the syntactic model produced by the closed cell method in this study. In this study, small scale pumice stone was used which is observed to have a different structure in terms of internal micro voids in it. Pumice stone enhance the spongy form of the products with the existence of micro voids. Large reserves are being placed around Anatolian side which has young volcanic formations. Cappadocia region is one of that region for pumice stone source. According to chemical analysis pumice formations are rich in silica and have a perfect glassy structure. Because of its availability and structural status, its usage is more feasible than the other syntactic materials in Turkey. The density of the pumice stone is between 0,4-0,6 g/cm3 which reduces metal weight when they have combined together to form metal foam. This value is also in the range of other syntactic foam metal densities. Although graphite crucible were preffered in other studies, test specimens were produced in steel mold during foam metal production with pumice stone in this study. Aluminum 7075 was used and melted in graphite crucible. The reason of using 7075 aluminum is it can be heat treatable which enable to analyze heat treatment process after specimen production. Molten aluminum splitted in steel mold in the case of bottom and top side of aluminum is covered with pre-heated pumice stone. This enables that molten aluminum forced to both gravitational and anti-gravitational infiltration process. While pure 7075 aluminum density is around 2,80 g/cm3 aluminum foam with pumice stone specimens' density measured between 1,42-1,62 g/cm3. Density is measured by mass /volume in which mass is measured in precision scale while volume calculated in cylindrical shape by measuring size with a digital calipper. Produced specimens inspected in the size of macro view with a detailed photography and micro size under optical microscope. Subsequently, specimens divided into two different group an done of them involved in T6 heat treatment process. Then, compressive stress test was applied to analyze heat treatment effect. The reason why compression test is applied to specimen is to analyze ability of stress that specimens resist. When a compressive load is applied to foam metal, the cell walls between the pores are subject to high compressive stress and deform locally and substantial deformation proceeds layer by layer. Through the continuous formation of these deformed layers perpendicular to the direction of compressive loading, a plateau region with approximately constant compressive stress appears. The plateau stress is defined as the average value of compression stresses for a compressive strain of 0.2- 0.3, and the energy absorption can be evaluated for a compressive strain between 0-0.5. Stress and strain curves data imported from compression test machine and plateu stress of each samples have been compared. Also area under the curve is calculated with the help of Excel and Matlab and valueas between the samples compared. This value is also called as absorption capability of specimen. This study does not cover all the alternatives and complexities in order to produce different specimen and manufacturing techniques. There is a huge opportunity to deal with foam material production and its characterization analysis. Different manufacturing approach and different pre&post process can be applied. Anyway, it will be much more valuable to do that in a specific target given by customers or university researches. Considering composite material industry, foam metal will be one of the most popular alternative for designers and manufacturers. It is not wrong to say that metallic foam products can be applicable currently most of the structural mechanical parts. Its sure that their application to dynamic mechanical parts will change the route of design studies. As pumice stone can be provided in natural way with a chargable cost interval which can be obtained in Turkey mining plants located around Anatolian side its popularity will increase starting from local manufacturers. The latest cost range is varying between 650-750 Turkish liras/ton excluding transportation costs according to mining company which pumice stone provided for this study. Whenever successfull attempt will ocur in foam metal industry, this will courage others to focus on that area. This will increases will not affect only metal industry but also pumice stone popularity which currently being used chemical, textile and construction industry. The speed of implementation of pumice stone into metal industry in Turkey will be higher than other countries as pumice sources are widely available in Turkey. It is expected that this study will support next foam metal research and pumice stone related investigation which will involve in metal based products in future.