MICROSTRUCTURE, CASTABILITY AND MECHANICAL PROPERTIES OF A201 ALLOYS WITH ADDITIONS OF Si, Ti AND B

Seminars
04.01.2018
14:30
David Wang Auditorium, 3rd floor Dalia Maydan Bldg.
Ms. Suzan Abd el Majid, Ph.D Candidate

Ms. Suzan Abd el Majid, Ph.D Candidate

Department of Materials Science & Engineering .Technion – Israel Institute of Technology
eng.suzan26@gmail.com

The additions of silicon, titanium and boron to the Al-4.97 wt. % Cu – 0.56 wt. % Ag based alloys (A201) were used to improve the castability, mechanical properties and microstructure of A201 alloys. The four alloys:A201, A201+Si, A201+Ti+B and A201+Si+Ti+B were investigated in the as-cast, solution treated at 550˚C for ~20 hours and aged at 170˚C up to 32 days conditions. The microstructures were investigated by a combination of HRSEM, TEM and EDS to reveal the effect of precipitation on the mechanical properties of the alloys. The as-cast alloys contained α-Al as a matrix and eutectic structure (α-Al/θ-Al2Cu) along grain boundaries. Addition of 1 wt. % of Si decreased the amount of pores; additions of 2, 4 and 6 wt. %Si improved the fluidity, prevent hot tears, but generate a lot of pores along GBs, then decreased the mechanical properties of the alloys. Additions of Ti and B cause the grain refinement, prevent hot tears, but cause a large amount of Al3Ti phase which makes the melt more viscose, resulting in decrease of fluidity and castability.

After solution treatment the eutectic structure at the GBs dissolved and an intermetallic phase α-Al15(Fe,Mn)3Si2 with faceted {112} planes, appeared.

The precipitation sequence during aging is the following: Supersaturated Solid Solution (SSSS) -> GP zones -> θ” + Ω -> θ’ -> θ. At the maximum hardness there are two kind of precipitates: θ” (Al3Cu tetragonal, coherent) and Ω (Al2Cu -Orthorhombic, semi-coherent).
The Si addition caused a large amount of θ” precipitates at the initial stage of aging and, by these means, increased the microhardness, also inhibited the formation of Ω phase. The additions of Ti and B (without Si) caused a large amount of semi-coherent Ω precipitates in expense of θ’ phase.
The A201 + 1%Si showed the optimal combination of mechanical properties and corrosion resistance

Advisor: Prof. Menahem Bamberger, Dr. Alex Katsman