Interaction of 308 stainless steel insert with A319 aluminium casting alloy

Abstract

In the metallurgical connection of aluminium alloys to steels, it is important to restrain the formation and growth of hard and brittle intermetallic phases at the aluminium/steel interface to enhance the mechanical behaviour of the joint. The influence of two coating materials, electroless plated copper (for 20 and 40 min) and galvanised zinc (at 480 and 550°C), on the quality of the interface between 308 stainless steel and A319 aluminium matrix was investigated. Copper led to the formation of a compact, solid inhibition layer against the elemental diffusion at the aluminium–steel contact temperature, while zinc resulted in the formation of a composite intermetallic layer which was open in structure. Comparing all interfaces formed between the insert and Al matrix, the 40 min Cu coated steel revealed the lowest values in terms of the thickness and microhardness after immersion into the molten aluminium.

Effects of steel type and sandblasting pretreatment on the solid-liquid compound casting characteristics of zinc-coated steel/aluminum bimetals

“…It is observed that Zn coatings on steel surfaces have many beneficial influences on aluminum/steel bimetal joining characteristics. However, interestingly, many studies on aluminum/steel joining except diffusion bonding processes as well as the present study have reported that Zn atoms are hardly detected at interfacial intermetallic phases [12,13,28,39]. The reasons for that are tried to be explained in relation to the behavior of Zn coating layer as follows.…”

“…This method is a very attractive manufacturing process for automotive components with complex shapes due to the benefits of cost-effectiveness, high production rate, and net shaping capability [11]. Despite these many benefits, it still remains difficult to get the aluminum to firmly join to steel inserts because of oxide scales on steel surface and large differences in the thermal-physical properties between those two metals, such as melting point and thermal expansion coefficient, which lead to poor wetting and metallurgical bonding [12,13]. Especially, in a form in which aluminum and steel are layered in parallel, rather than a form in which steel is embedded in aluminum, their joining becomes much more difficult because the shrink fitting effect is not available.…”

“…In the case of compound casting, the whereabouts of Zn coating layer was unclear: on compound casting of Al 0.4%Si alloy and zinc-coated steel with 300 µm thick Zn coating, Zn atoms were observed in the interfacial intermetallic phases [14], while using Al 6.8%Si alloy and zinc-coated steel with 300 µm thick Zn coating, Zn atoms were not observed in the bonding zone [13]. To simulate a compound casting process, Khoonsari et al [12] conducted an immersion test,…”

“…14 and 17). Steel/aluminum bimetal systems are known to have a narrow processing window for bonding: they are hard to be metallurgically bonded because of the high steel surface oxidation tendency and the much different thermalphysical properties between those two metals, but once the energy input is high enough to ignite the metallurgical bonding reaction, it is difficult to avoid an excessive formation of brittle interfacial reaction layer due to the rapid growth kinetics of intermetallic phases [12,13,29]. In addition, controlling the bonding reaction rate only by the superheat temperature of aluminum alloy melt may cause another problem, i.e., too high superheat temperature creates the aluminum alloy melt oxidation, porosity defects, etc., and in revere, too low superheat temperature makes it difficult to cast complex shaped parts with large area and various casting thickness, especially thin casting section.…”

Microstructural and mechanical characterization of a stainless-steel wire mesh–reinforced Al-matrix composite: Bimatallic components for lightweight design

“…The reaction layer thickness increased significantly (80 m) after heat treatment at 540 °C for 2h with cracks appearance that, de facto, weekend the interface bonding strength. The composition and microstructure of intermetallic compounds (IMC) formed at the interface between aluminum alloy AA4343 and stainless steel SUS316 upon annealing at 550 •C for 1h to 20h and at 610 •C for 15min to 10h were recently studied by Zhang et al [32]. The reaction layer after solution at 550 °C for 10h was constituted above all by τ10(Al4Fe1.7Si) and η(Al 5 Fe 2 ); its growth kinetics followed the rational equation x = (kt) n , where x is the layer thickness, t is the time and k and n are two constants.…”