Influence of high-pressure die casting parameters on bonding characteristics of aluminium-steel hybrid-castings for automotive lightweight structures

Abstract

For automotive lightweight design, aluminium and steel bi-metallic structures are being increasingly applied. Aluminium-steel hybrid-casting is one of the coming technologies. To achieve a firm bonding between both materials, a new AlSi(Fe) coating was developed and analysed in previous works showing approximately 10 MPa shear strength and high ductility. In this work, a systematic study has been conducted on hybrid-casting of DP800 steel in an AlSi10MnMg alloy using high-pressure die casting (HPDC) trials, its thermal analysis, and mechanical tests on different types of hybrid-cast specimens along with finite element (FE) casting simulation and scanning electron microscopy (SEM) analysis on tested specimens to understand the entire process chain. It was found that the mould temperature is the most important parameter, and the second one is the preheating temperature for the steel insert. With 280 °C mould and 500 °C preheating temperature, and >40 m/s injection gate velocity, the shear strength can be increased to 15 MPa with considerable plastic deformation of the bonding layer and small scatters. Three fracture surface types can be observed by SEM, and clearly understood by considering the temperature profile of the steel inserts during the casting process that can be determined using FE casting simulation calibrated by die casting tests. These findings on shear specimens were further validated by pullout tests with overlapped metallurgical and force-fit bonding, as well as cross-tension tests. Together with force-locking the total bonding strength achieves 25 MPa.