ENERGY ABSORPTION CHARACTERISTICS OF DUCTILE AlSi4MgMn AND AlSi9MgMn DIE-CASTINGS INVESTIGATED BY SHEAR BOLT TESTING M. C. Srivastava and O. Lohne Department of Material Science and Engineering, NTNU, Trondheim, Norway Copyright Ó 2016 American Foundry Society DOI 10.1007/s40962-016-0073-z Abstract The energy absorption of high-pressure die-cast AlSi4MgMn and AlSi9MgMn alloy samples is investigated in the as-cast, and solutionised and 4 h aged condition using a shear bolt test. The shear bolt test is not a standard technique to test the properties of the material, but can be used to evaluate the energy absorption of the material. The microstructures of the as-cast and heat-treated specimens are examined. The fracture surfaces are investigated using scanning electron microscopy to understand the fracture mechanism during the shear bolt tests. The heat treatment is expected to give better properties owing to, i.e., spheroidisation of Si particles and subsequent age hard- ening due to the presence of Mg in the alloy. It is observed that there is 10–30 % improvement in energy absorbing capacity of the material after ageing. Keywords: high-pressure die-casting (HPDC), AlSiMgMn alloys, shear-bolt testing, energy absorption, fracture surface, microstructure Introduction High-pressure die-casting (HPDC) is a manufacturing process in which molten metal is injected, under pressure, into a hardened steel die. The metal solidifies in the oil- tempered die which is then opened, and the die-casting is ejected. The ejected castings are quenched sometimes depending on the end requirement. Automotive compo- nents made of light alloys are increasingly being produced using the HPDC method owing to growing concern for the economy and environment. 1,2 The turbulence in the melt flow within the die may give rise to entrapment of gas having little time to escape during die filling. This may result in the formation of porosity in the castings. The entrapped gas facilitates shrinkage porosity. 3 The HPDC material is characterised by variations in the mechanical properties. Some of the factors affecting these variations in the properties are the difference in local heat transfer rate 4 and complex geometry of the integrated cast components having different thickness and shape. The die-cast material has fine grains that help in obtaining superior mechanical properties of material compared to gravity-cast material. In previous work, the present authors have investigated the HPDC material (AlSi7MgMn) using Charpy and tensile testing. 5 In the follow-up work, a low-temperature solution treatment and subsequent ageing are presented for HPDC AlSi9MgMn alloys to improve the strength of the mate- rial. 6 In the Charpy testing of grooved specimens, the material fails at the notched area. In the notched Charpy testing, a weakest area is introduced into the sample arti- ficially. In the tensile testing, the material fails from the weakest area of the specimen, depending on the presence of local defects such as pores or inclusions. The properties obtained in both these tests are based on the weakest area of the material. The shear bolt test that is carried out here, gives an average property of the material tested. 7 A shear bolt test records the energy absorbed during fracture and takes care of local property variations in the HPDC material and maps the overall characteristic of the material. More and more die-cast components are being used in automotive structural parts. 8 It is therefore a necessity to improve the energy absorption capacity of the die-cast components for safety reasons. In this work, the energy absorption potential of HPDC plates made of the alu- minium alloys AlSi4MgMn and AlSi9MgMn has been investigated in the as-cast and stored, and the heat-treated International Journal of Metalcasting