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In-situ formed, ultrafine Al-Si composite materials: ductility

Guba P., Gesing A., Sokolowski J., Conle A., Sobiesiak A., Das S., Kasprzak M.

Journal of Achievements in Materials and Manufacturing Engineering

2019

Vol. 92, nr 1-2

5--12

Purpose: The work objective includes optimization of the casting production and heat treatment processes that will simultaneously maximize the combination of strength, hardness, and ductility for hypereutectic Al-Si compositions with Si volume fractions of as much as 25 vol.%. In addition, such an in-situ formed composite alloy will attain a unique combination of low production cost, high potential recycled content, and functional characteristics suitable for mission critical aerospace and vehicular applications. Design/methodology/approach: The unique High Pressure Die Casting Universal Metallurgical Simulator and Analyser (HPDC UMSA) was used for melting, cyclic melt treatment, and solidification of the hypereutectic Al-Si-X (A390). The produced as-cast structures contained colonies of nano-diameter Si whiskers and other morphologies, and absence of primary silicon particles. Heat treated structures rendered nano and ultrafine metal matrix composites. Findings: New developed as-cast Al-Si materials containing nano-diameter Si whiskers, without primary silicon particles required ultra short time heat treatment to result in nano and ultrafine metal matrix composite, rendering their hardness, strength and wear resistance, and the same time retaining toughness and ductility. Research limitations/implications: The cast samples were produced in laboratory conditions and potential tensile strength was estimated from empirical correlation with micro-hardness measurements. In the future, the comprehensive mechanical properties need to be tested. Practical implications: These ultrafine Si, Al-MMCs can be net-shape formed by modified HPDC technology or consolidated from spray-atomized alloy powder. Originality/value: Optimization of the entire production process for the hypereutectic Al-Si alloy compositions achieved a uniform distribution of ~ 25 vol.% of ultrafine Si particles in ductile FCC-Al matrix further reinforced by age hardening with nano-scale spinodal GP-zones. The associated mechanical property and ductility improvements will open a wide range of critical lightweighting components in transportation: aerospace, terrestrial vehicle and marine to the optimized hypereutectic Al-Si alloys. Presently, these components do not use the commercial HPDC A390 alloys due to their limited ductility and strength. Proposed new technology will allow conversion of various cast airspace alloys with ultrahigh mechanical properties to the automotive applications.

Combined thermal, microstructural and microchemical analysis of solidification of Al25Si3Cu alloy

Guba P., Gesing A., Sokolowski J., Conle A., Sobiesiak A., Kasprzak M.

Archives of Materials Science and Engineering

2017

Vol. 85, nr 2

49--79

Purpose: This paper present thermal and microstructural and microchemical analyses were conducted on the unmodified experimental alloy Al20Si3Cu (B390.1) solidified in the High Temperature Universal Metallurgical Simulator and Analyser (HT UMSA) under atmospheric pressure (0.1 MPa) and a relatively low solidification rate (-1.2 K/s just after end of solidification), for identification of the thermal events during solidification and the phases in the as-cast structure. Design/methodology/approach: The HT UMSA platform, using a low thermal mass stainless steel cup, enabled the acquisition of high resolution thermal analysis data. Design/methodology/approach: A new approach for de-convolution of the first derivative thermal curves allowed detailed thermal and microstructural phase histories to be documented for solidification of Al-Si alloys. Recently developed SEM/EDS methodology allowed to determine composition and distribution of individual phases that are smaller than the X–ray volume. Findings: Simultaneous consideration of thermal microstructural and microchemical information allowed detailed understanding of the series of events that take place during solidification of Al casting alloy with complex chemistry. In our hypereutectic alloy we document growth of Al(1) dendrites and formation of secondary Si(2) and Al(2) phases all at temperatures higher than the binary equilibrium Al-Si eutectic temperature of 850 K. Practical implications: Even at this slow solidification rate detailed understanding of the solidification microstructure requires consideration of non-equilibrium processes during solidification. Originality/value: We propose an original set of hypotheses that consistently explain the observed non-equilibrium solidification behaviour. Proof of these hypotheses is beyond the scope of this work.