Improvement of Al-6061 alloys mechanical properties by controlling processing parameters
— this paper discusses the effect of casting processing parameter on the mechanical properties of Aluminum alloy 6061 companied with Al 2 O 3 and Si C P. The specimens were poured in two different mold types one of steel and the other of graphite. These two types have a wide range of cooling rate; steel has fast cooling rate whereas graphite has slow one. In order to investigate this effect, and the alloying elements participation the specimens were taken from three different positions in the mold; top, middle and bottom. The mechanical wear, hardness and microstructure examination were performed. The results showed that wear rate and hardness increase in case of specimen poured in steel mold. This increasing due to fast cooling rate which make refining of the grain size of aluminum alloys. Whereas, their mechanical properties decreased when using graphite molds. In contrast of this result, ductility is increased. This is attributed to that graphite has slow cooling rate (heat dissipate is low) which make enlargement to the grain size of aluminum alloy and the graphite is also solid lubricate playing as interactive lubricate which is main reason to decrease the wear rate.
Optimization of Mechanical Behaviour of AA 5083 Nano Sic CompositesUsing Design of Experiment
Composites with aluminium alloy matrix and ceramic reinforcements are popular candidates in automotive, aerospace, defense and other industries because of their high strength-toweight ratio, stiffness, impact strength, wear resistance, etc. In the present study AA 5083/Nano SiC composite were fabricated by stir casting. A 2-level Full Factorial design of experiments (DOE) was used to study the influence of process parameters like casting temperature, stirrer speed, and weight percent of reinforcement on hardness of composites. Mathematical model was developed to investigate which parameters significantly affect the hardness of composites. The effect of parameters on the response and adequacy of hardness model developed were tested by employing ANOVA and Fisher’s F-test. This model can be used to select the optimum process parameters for obtaining the composites hardness within the range of experimental frame work.
Effect of alloying elements on the segregation and dissolution of CuAl2 phase in Al-Si-Cu 319 alloys
The hypoeutectic 319 aluminum alloy (Al-7%Si-3.5%Cu) was used in the present study to investigate the effect of diverse alloying elements on the dissolution of the copper phase (CuAl2) during solution heat treatment. Elements such as Sr, Fe and P were added to the base alloy individually and in various combinations. The cooling curves of these alloys were obtained by solidifying the alloy melts in a preheated graphite mold (600°C, cooling rate ∼0.8°C/s). From these the first derivate curves were plotted and used to determine the effect of the additives on the precipitation temperature of the Al-CuAl2 eutectic reaction. Microstructural examination was carried out using optical microscopy, image analysis, and electron probe microanalysis (EPMA), with energy dispersive X-ray (EDX) and wavelength dispersive spectroscopic (WDS) analysis facilities. Samples from different alloys were solution heat treated at 505°C for various times up to 100 hours. The results explicitly reveal that solution heat treatment plays a critical role on the dissolution of the CuAl2 phase. It is found that Sr leads to segregation of the CuAl2 phase away from the Al-Si eutectic regions, which slows down its dissolution during solution heat treatment. The β-Al5FeSi phase platelets act as preferred precipitation sites for the copper phase and hence lessen the degree of segregation. Thus, addition of Fe can accelerate the copper phase dissolution. However, phosphorus addition has a negative effect on CuAl2 dissolution due to (i) its solubility in the CuAl2 phase particles, and (ii) the formation of (Al,P)O2 oxide particles which act as nucleation sites for the precipitation of the block-like CuAl2 phase. It retards the complete dissolution of this copper phase even after 100 hr solution treatment. In the case when phosphorus and iron are added together, the negative effect of phosphorus can be neutralized to some extent.