Foaming of Friction Stir Processed Al Precursor by Microwave Heating

Abstract

A substance with pores (voids) is known as a porous medium or material. The skeleton element of the substance is frequently referred to as the "matrix" or "frame." Many naturally occurring materials, including rocks and soil (such as aquifers and petroleum reservoirs), zeolites, biological tissues (such as bones, wood, and cork), and man-made materials, including metal, cement, ceramics, and polymers, can be categorized as porous media. These cellular materials are typically utilized in cases where weight needs to be reduced. Metals have a high energy absorption capacity during deformation caused by dislocation motion. As a result, metallic foams might offer an engineering material with the beneficial mechanical characteristics of polymeric foams, making them useful in applications where higher yield stresses and energy absorption are required. For many years, material scientists and technologists have worked to develop porous metals and metal foams. Metal foam is mainly composed of liquid and solid phases that coexist in a specific structure. A gas source is utilized to introduce pores into the structure. This gas source could be a blowing agent powder added to a liquid metal at a specific temperature, direct gas bubbles introduced to a liquid metal, or a blowing agent powder imbedded in the metal that expands when heated. In the current technique, Titanium Hydride (TiH2: blowing agent), Aluminum powder (Al powder) and Calcium Carbonate (CaCO3: stabilizing agent) is embedded in the Aluminum AA7075 and AA6063 matrix using Friction Stir Processing (FSP) as the starting procedure. At this point, the metal is referred to as a precursor. This precursor creates a porous structure after being heated in a furnace/microwave at a specific time and temperature for the decomposition of the TiH2. As a result of this decomposition, hydrogen gas is released, which remains in the matrix and forms pores. Metal foam is created when these holes have a spherical shape or a design that causes the density to be significantly reduced. The results of various experiments such as powder filling techniques, tool pin profiles, and a new precursor development technique called as Friction Stir Deposition (FSD) are reported in this research work in order to ensure uniform TiH2 distribution throughout the aluminum matrix for producing closed cell aluminum metal foam and its characterization. This indirect foaming method prevents the early melting of the material. This procedure opens the way for the creation of effective localized foam parts. Based on the characteristic of the developed foam, it has been observed that the distribution of foamable mixture improved in the buried hole technique by creating an entrapped space to restrict the mixture to flow away and produce a porous Aluminum with a porosity of approximately 81% at 4-passes with 40% TiH2 composition. As the number of FSP passes increases, pore size decreases. The percentage decrease in pore size from one pass to four passes during microwave heating is observed as 17.78 % as compared to 14.76 % in furnace heating. The time required for the development of foam in microwave heating is lower than that of furnace heating and the time needed for the development of foam in microwave heating is only 16.67% of the furnace heating. It is also observed from the results that the porosity in sandwich and groove techniques is 69% and 48%, respectively. The buried hole technique has higher porosity and improvement in porosity is of 17.92% and 71.25% as compared to sandwich and groove techniques, respectively. It is also observed that during different tool pin profiles, the distribution of the foaming mixture improves with continuous material deformation by straight threaded cylindrical (STC) tool pin compared to the pulsating effect produced by square (SQ) and triangular (TR) pin. The foam developed at straight threaded cylindrical (STC) pin shows uniform deformation behavior during compression test than the foam developed by other tool profiles. The foam developed by friction stir deposition (FSD) technique shows uniform distribution of foaming powder in 4 and 5 numbers of holes in the consumable rod as compare to other. The hardness of the deposited precursor is lower than the base metal. The deposited material shows equiaxed fine grains that occurred due to dynamic recrystallization during deposition also have longer plateau stress due to optimum pore size which absorbs energy for longer duration.