The Influence of Iron Concentration on the Mechanical Properties of A356 Al Alloy for Car Rims Application

Abstract

A356.0 aluminum-silicon alloy is a base material for car rims application. Car rims are critical components for a vehicle as they carry the load of the passengers, goods, and the weight of the vehicle itself, therefore they should be sufficiently strong to withstand the vertical load, fatigue load, impact load, the side load and the braking force. Car rims are made by gravity die casting process. During the casting process, the inclusion of iron-content parts entering the molten Al can take place which leads to higher iron (Fe) concentration. High Fe con concentration lowers the toughness and the ductility of car rims. This study investigates the maximum value of Fe concentration that can be tolerated for acceptable mechanical properties of Al-Si alloy A356.0 for car rims application. The Fe concentration studied was 0.12 %wt, 0.16 %wt, and 0.20 %wt. Evaluation was performed on tensile and impact properties of the specimens. The test results show that increased Fe concentration decreases elongation, yield strength and ultimate tensile strength (UTS). Furthermore, there is a quite large decrease in UTS (by 34 MPa) when Fe concentration increases only by 0.06 %wt. Impact strength decreases significantly from 15.47 to 2.91J/cm 2 as Fe concentration content increases from 0.12 %wt. to 0.16 %wt. The porosity present in the casting is predicted to contribute to the ductility decrease. In addition, the decreasing value of UTS is predicted due to grain growth and dendrites formation. It is recommended that the maximum allowable Fe concentration for car rims application is 0.12 %wt. 1. INTRODUCTION Nowadays various Al (Al) alloys are used for various engineering applications including in the transportation industry. Due to economic and technical consideration, lighter vehicle is required and regulated. One strategy to achieve the lightweight vehicle is by employing Al-based alloys for several auto parts, like the engine blocks and wheel rims. Al alloy A356.0 is used widely in aerospace and automotive application. Although Al alloy cannot be applied for heavy vehicle e.g. rims of bus and truck, aluminum-silicon (Al-Si) A356.0 is widely used for car rims application. The A356.0 alloy fits to be used for car rims since it shows good mechanical behaviors, i.e. high strength-to-weight ratio, corrosion resistance, and good castability. On the other side, car rims should show good resilient, resistant to side load or braking loads properties, have good tensile properties. According to Japan Industrial Standard (JIS) H 5202, material for car rims should possesses elongation > 5%, ultimate tensile strength (UTS) > 245 MPa, impact strength higher than 5.90 J/cm 2 [1]. These mechanical properties however cannot be achieved only by as-cast product. Thus, Al car rims must undergo heat treatment to achieve those mechanical properties. Alloying elements added to the molten Al during casting influence the mechanical properties and heat treatment ability of as-cast Al.