Thermal Analysis

THERMAL ANALYSIS OF Al 2014 REINFORCED WITH

ALUMINA (Al2O3) PARTICLE COMPOSITES

M.N. Mazlee
School of Materials Engineering
Universiti Malaysia Perlis (UNIMAP)

Malaysia

mazlee@unimap.edu.my

The precipitation hardening of the matrix alloys was controlled by the presence of the ceramic reinforcements. The addition of a brittle ceramic reinforcement to a precipitation hardenable alloy can significantly alter the nucleation and growth kinetics of precipitation in the matrix as compared to the unreinforced alloy (1). An acceleration of the precipitation sequence in metal matrix composites (MMCs) was observed as a result of enhanced precipitation nucleation on dislocations due to the coefficient of thermal expansion (CTE) mismatch (2,3).

The thermal analysis studies have been carried out on the Al 2014 matrix composites reinforced with 10 volume percent (hereinafter noted as Composite 1) and 15 volume percent (hereinafter noted as Composite 2) of alumina (Al2O3) particles respectively. The effect of alumina particles on the precipitation phases and phases transformation of Al 2014/Al2O3 MMCs was studied using differential scanning calorimetry (DSC). DSC thermograms in Figures 1 and 2 have shown the formation and dissolution phases in Composite 1 and 2.

Composite 1 and Composite 2 were found to have 4 phases and 3 phases of zone formation respectively and 2 phases each of dissolution zone. From DSC thermogram, it was revealed that the sequence of precipitation hardening for Composite 2 was similar to that of Al-Cu alloys; supersaturated alpha -- Guinier-Preston (GP) zone -- theta" -- theta' -- teta. Comparatively, the precipitation of GP zone and metastable phases for Composite 1 and 2 was faster compared to that of Al-Cu alloy (4).

From the microstructure, the deformation banded structure in Composite 2 was shown in Figure 3. The deformation banded structure is believed to be one of the factors which contributes to the accelerated precipitation process in Composite 2. The dilatometer is used to measure and record the change of the length of the composites. The CTE data was acquired using the LINSEIS L75 dilatometer. From the thermal expansion test (Table 1), it was found that the values of CTE of Composite 1 and Composite 2 were not much different. However, the CTE of the composites was lower than the unreinforced Al 2014 alloys (23.20 x 10-6/°C).

References
1. Suresh S. and Chawla K. (1991), Fundamentals of Metal Matrix Composites, Oxford: Butterworth Heinemann.
2. Shamsul J.B. (1998), The Characterisation and Properties of Aluminium Matrix-SiC Composite, PhD Thesis, University of Leeds, UK.
3. Arakawa S., Hatayama T., Matsugi K. and Yanogisawa O. (2000), Scr. Mater., 42, 755-760.
4. Hong S.K., Hwang S.H., Choe J.C., Park I.M., Tezuka H., Sato T. and Komino A. (1997), Material Science Forum, 242, 165-172.