Growth behavior of intermetallic compound layer in sandwich-type Ti/Al diffusion couples inserted with Al-Si-Mg alloy foil

Abstract

Titanium has been widely used for airplane and space activities as a light and high temperature structural material due to its high specific strength and high corrosion resistance. Recently, it has been necessary to join titanium to other metals, such as aluminum, mild steel, and copper [1–3]. Hence, it is necessary to investigate and develop joining techniques that can be applied relatively easily. Liquidus diffusion bonding is beneficial to join many contact points simultaneously without severe distortion, which has been widely adopted in dissimilar metal joining. However, one of the problems in dissimilar metal joining is the formation of a brittle reaction layer in the joint interface. The growth of such a reaction layer reduces the mechanical properties of the joints. Therefore, it is necessary to investigate the growth mechanism of the reaction layer at the joint interface. Some authors have explained the growth behavior of intermetallic compound, Al3Ti, during interaction between pure Ti and pure Al using Ti/Al diffusion couples [4–6]. Similarly, this diffusion reaction is supposed to occur during liquidus diffusion bonding of Ti/Al with Al-10Si-1Mg filler metal. In this work, we investigate the growth behavior of the reaction layer during the diffusion reaction between Ti, Al and Si using sandwich type Ti/Al diffusion couples inserted with Al-10Si-1Mg alloy foil and their resulting microstructure. The base materials used in the present work were 3003 aluminum and pure titanium. The chemical composition and liquidus temperature of the insert metal were Al-10Si-1Mg (wt %) and 582 ◦C, respectively. Before the preparation of the diffusion couples, the titanium and aluminum base metal were pretreated by abrasion on 800-grade silicon carbide paper, and then immersed in 5%HF-5%H2O2 aqueous solution and in 10%NaOH-10%HNO3 aqueous solution to remove surface oxides, respectively. A sandwich-type diffusion couple of pure Ti/Al-10Si-1Mg alloy foil (100μm)/ 3003 Al was set and a uniaxial pressure of about 0.4 MPa was applied. The diffusion couples were heated in the temperature range of 560–640 ◦C for 30 min in vacuum. The temperature was measured by a Pt-Pt (10%Rh) thermocouple spot-welded close to the interface. The interface microstructure of the couples was examined by scanning electron microscopy