The properties of hot extruded binary magnesium calcium alloy for use as a biodegradable material within bone

• Main Author: Mirshahi, Mohammad
• Format: Thesis
• Language: English
• Published: 2010
• Subjects: TJ Mechanical engineering and machinery
• Online Access: http://eprints.utm.my/id/eprint/16648/1/MohammadMirshahiMFKM2010.pdf; http://eprints.utm.my/id/eprint/16648/; http://dms.library.utm.my:8080/vital/access/manager/Repository/vital:83049?queryType=vitalDismax&query=The+properties+of+hot+extruded+binary+magnesium+calcium+alloy+for+use+as+a+biodegradable+material+within+bone&public=true

The development of the suitable strategies to enhance the normally poor corrosion resistance and mechanical properties of magnesium alloys is an important issue that must be solved in order that magneiusm-based materials have wider biomedical applications. The work described in the thesis consists of two processing part: 1) Mg-xCa alloy preparation; in which five different mixture of commercially pure Mg (99.999% ) and granules of Mg-40%Ca were die-cast and 2) extruding one of the as-cast Mg-xCa alloy from the casting process with optimum properties resulted from tests accomplished, at ram speeds of 26, 52 and 65rpm and temperatures 250°c, 350°c and 450°c. Optical microscopy observations of as-cast products and compositional analysis accomplished by EDS and X-RD showed that Mg-xCa (x= 0.7%, 1%, 1.9%, 2.8% and 3.6%) were composed of two phases, a(Mg) as the grain matrix and Mg2Ca on the grain boundaries. The hardness test results also showed that the Vickers hardness rates will increase by increasing the Ca content in the Mg-Ca alloys which was mainly due to the grain refinement and increment of Mg2Ca volume hindering the dislocations movements; According to the corrosion potential values, in-vitro corrosion rate and pH values, it was found out that binary Mg-Ca alloys with greater Ca contents corrodes faster than alloys containing less Ca; thus, increases the pH of the SBF solution and hydrogen evoluted from cathodic reaction more than others, that is predominantly due to grain refinement and increased Mg2Ca by adding more Ca. Finally by comparing the results acquired from tests and findings of Li et al. (2008) the Mg-1%Ca was selected as the the best compromise between mechanical properties, degradation behavior and biocompatibility of the implant. Since the higher ram speeds in extrusion develop finer grain structure (Y. Uematsu et al. 2006) it was expected that the corrosion rate decreased by grain refinement, but based on the results of electrochemical and immersion test conducted on as-extruded Mg-1%Ca products, the corrosion rate is lowest for the temperatures around 350 ºc and ram speeds of approximately 50 rpm. The hardness rates of the samples were enhanced at higher ram speeds and lower processing temperatures which is mainly because of grain refinement and possible phase precipitations.