The Effects of Two-Step Solution Heat Treatment of Al-6Si-2Cu Alloy for Lightweight Automotive on Mechanical Properties

Abstract

The effects of two-step solution heat treatment of aluminum alloy for lightweight automotive have been investigated. The test specimens, Al-6Si-2Cu alloys are prepared by gravity casting process. Solution heat treatments in this study are applied to improve of mechanical properties through a single-step or two-step solution heat treatment. For the microstructural characterization, inductively coupled plasma mass spectromerty (ICP-MS), optical microscope (OM) and scanning electron microscope (SEM) analyses are conducted in specimen. The X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) analyses are also applied to identify the intermetallic phases with quantitative and qualitative analyses. Micro Vickers hardness and static tensile test are achieved. The microstructure of gravity casting specimen represents a typical dendrite structure having a secondary dendrite arm spacing (SDAS) of 37um. In addition to the Al matrix, a large amount of coarsen eutectic Si, Al2Cu intermetallic phases and Fe-rich phases are identified. After solution heat treatment, the mechanical properties of two-step solution heat treatment alloy show higher values than as-cast and single-step solution specimens. Consequentially, the two-step solution heat treatment could be used in automotive parts to improve mechanical properties.