17.4 Conclusions Composites AA7075/27 wt% of low density, foamed SiO2/Al2O3/Fe2O3 particles, produced by thixoforming present wide plateau of plastic deformation under compression at low stresses, which gives the material ability to absorb energy in potential applications such as in impact situations. Solubilising/ageing treatments can improve compression behaviour of the thixoformed composite, which presents in this condition coarse boundaries in the alloy microstructure. Results indicate that solubilising conditions investigated (470 C/12 h) was not able to promote complete dissolution of secondary phases but even so significant increase in σmax andσpl was reached. Micro hardness of the metal matrix and plastic deformation of the material were not so affected. Ageing conditions investigated (170 C/24 h) promoted significant increase in σmax (100 %) and σpl (400 %) when compared to thixoformed condition. Reduction of only around 14 % in plastic deformation was observed. This behaviour indicates high ability of energy absorption during mechanical solicitations under compression not only at low stresses. 0 20 40 60 80 100 120 0 5 101520253035404550556065 Stress (MPa) Deformation % As-thixoformed 0 20 40 60 80 100 120 0 5 101520253035404550556065 Stress (MPa) Deformation % Solubilised 0 20 40 60 80 100 120 0 5 101520253035404550556065 Stress (MPa) Deformation % Aged a b c Fig. 17.7 Stress deformation curves in semistatic compression tests of AA7075/cinasite composites in different conditions: (a) as-thixoformed; (b) after solubilising (470 C/12 h); (c) after ageing (170 C/24 h) 17 Influence of Heat Treatments on Microstructure and Mechanical Behaviour of Compressible. . . 147
RkJQdWJsaXNoZXIy MTMzNzEzMQ==