Studying the effect of Different wt % AL 2 O 3 Nanoparticles of 2024 Al Alloy / AL 2 O 3 Composites on Mechanical Properties

The nanocompsite of alumina (Al2O3) produced a number of beneficial effects in alloys. There is increasing in resistance of materials to surface related failures , such as the mechanical properties , fatigue and stress corrosion cracking .The experimental results observed that the adding of reinforced nanomaterials type Al2O3 enhanced the HB hardness, UTS, 0.2 YS and ductility of 2014 Al/Al2O3 nano composites . the analysis of experiments, indicated that The maximum enhancement was observed at 0.4 wt.% Al2O3. The ultimate improvement percentage were 15.78% HB hardness, 18.1% (UTS), 12.86% (0.2 YS) and 25.71% ductility. These enhancements in the above properties maybe to high dislocation density resulting in good bounding between Al2O3 and metal matrix.


Introduction
Most engineering components which operates in the fields of aerospace, automotive and marine applications need to improve their mechanical properties like tensile strength, yield strength, hardness and strength to weight ratio.A composite is a material which consists of two or more combined elements.One is referred as matrix and the other is called reinforcing element.The reinforcing material may be in the form of fibers or flakes.The composites are divided into main branches depending on the chemical analysis of matrix element [1]. 1. Metal matrix composites (MMC ). 2. Polymer matrix composites.3. Ceramic matrix composites.Different reinforcement materials such as Si N , B C, SiC and AL2O3 used to improve the mechanical properties of the composites.A comprehensive review was done on the mechanical properties i-e strength to weight ratio and tribological properties [1].
M. Vykuntarao et al [2] studied the influence of various reinforced particles on the mechanical properties of aluminium based metal matrix composite using stir casting method and they found that increasing wt% of nanomaterial leading to improving the mechanical properties of composites.Also the finer size of reinforced particles the height composite mechanical properties.
Lakhvir singh et al [3] fabricated (MMC ) with three different wt% of AL2O3 particles reinforced in pure aluminium i-e 3,6,9 wt%.They found that the mechanical properties increased with increased the weight percentage (wt%).
Sajjadi et al [4] used two different sizes of reinforcement 20 µm (micro) and 50 nm (nano) of AL2O3 with aluminium alloy as matrix.It was observed that the compressive strength, and hardness of (MMN ) increased when the wt% of AL2O3 increased.Also the compressive stresses in nanocomposite were higher than those in micro composites.
Mazahery et al [5] tested Al (A356 alloy) / nano AL2O3 composites fabricated by stir casting technique using different volume fraction of nanomaterial.The experimental results revealed that the significant raising in hardness, ultimate tensile strength while the ductility was reduced.This improvement is resulted due to uniform distribution of reinforced material and refinement of aluminium matrix grains.
Baradeswaran et al [6] examined 7075 Al alloy/ AL2O3 composites manufactured by liquid metallurgy method.They observed experimentally that the ultimate strength (tensile and compressive), and hardness increased in a linear manner with increasing the AL2O3 wt%.
They found that 0.3% Wt. exhibited best mechanical properties of nanocomposites.
Alumina is a suitable choice as reinforcement due to its good mechanical properties and thermodynamic stability with aluminum.Aluminum /Al2O3 composite 10% wt. of 2014 with (20 -50 ) μm particle size .The expermantal analysis indicated that the composite exhibited higher mechanical properties such as yield and ultimate stress [8].

Experimental Details
The below tables describe the metal matrix with its physical and chemical properties and the nanomaterial reinforcement, the metal matrix Nano composites(MMNCs) preparation and testing The metal matrix The metal matrix used in this study was 2024/Al alloy.The chemical composition in wt.% is given in table (1) The 2024/Al alloy plates are used in fuselage structure, wing tension members, shear webs and ribs while sheets are usually used in commercial and military aircraft for fuselage skins, wing skins ad engine areas where elevated temperatures to 250 0 F (121 0 C) are often encounted [ 9] .
The mechanical properties of 2024-zero temper sheet and plates are given in table (2) mechanical properties of 2024-zero temper [9].

The Reinforcement Material
The reinforced material was Al2O3 with particles mean size of about (10) nm Table (3) shows the chemical composition of Al2O3 in wt.% [ 10 ].

Table 3, Chemical Composition of Al2O3 wt%
The mechanical and microstructural properties via volume % of nano Alumina (Al2O3) particles were examined by Mohsen and Mazahery [10] and tableted below in Bharath et al [ 13 ] tested the physical and mechanical properties of the reinforcement particles and found that density (gm/cm 3 )=3.69,Hardness (HB500)=1175 , Strength (MPa)= 2100C( compression) and modules of elasticity (GPa)= 300.It is clear that the presence of Al2O3 reinforced material in the composite lead to improve the mechanical properties because the Al2O3 particles itself relatively have high mechanical characterization as mentioned above

Preperation of Composite
The Alumina particles of about (10 nm) size were selected as a reinforced material due to the reasons [ 13 ] : 1-It has good thermal stability.2-Good wear resistance and high surface hardness.

3-Low in cost and available.
The MMCs reinforced with weight percentage (0.2 , 0.4 , 0.6 , 0.8 and 1.0) % of Alumina have been fabricated using the stir casting technique.Before introducing the Al2O3 particles into the melt, the particales were preheated to a temperature of 200 0 C and the stirrer was preheated before immersing into the melt, and running at speed of 450 rpm.The casting temperature of 850 0 C was adopted and the molten composite was poured into the cast iron moulds .Thus composite with 0.2 , 0.4 , 0.6 , 0.8 and 1.0 wt.% of Al2O3 were produced in the form of rods.The above melting for manfucacting the MMCs were mentioned in details in Ref [14] for the same authors using the manifesting test device for fabricating the MMCs composites.

Experimental Results Analysis and Discussions
Hardness  It is clear, form the figure (1) above, that the HB hardness increases when the wt.% of nanomaterial increases, the maximum increase of 15.9% is occurred at 0.4 wt.% Al2O3 compared to as cast.The results are in good agreement with the findings of Dinesh et al [11] who found that an increase of nearly 92% in hardness of Al. matrix -Al2O3 in comparison with pure aluminium.
Sajjadi et al [4] studied the hardness of aluminium matrix composites (AMCs) reinforced by Al2O3 the composites was chosen as: 3%, 5% and 7% (mass fraction).using stirring casting method and they concluded that the increasing of adding Al2O3 resulting in increase of hardness of composites.
M. Karbalaei A. et al [12] used A356 Al. alloy as matrix of Nano composites reinforced by Al2O3 using stir casting technique.They observed that the best hardness was obtained at 240 second of stirring time.But increasing the time of stirring leading to reduction in tensile properties of composite.
It is observed from figure ( 1 ), the maximum value of HB was found at 0.4% weight percentage of Al2O3, but all the values of Al / composites are higher than that of as cast.The main reasons of this improvement may be the followings: 1.The high hardness of Al2O3 itself could be attributed to increase the hardness of composite.Bharath et al [13] measured the HB (type 500) hardness of Al2O3 and recorded it to be 1175.2. The less porosity and the homogeneous distribution of nanomaterial lead to high value of hardness.Tsakiris et al [16] used high power milling method, They found that the optimum milling time leads to uniform distribution of Al2O3 particles and reduce the amount of porosity resulting in raising the hardness.

Tensile UTS and yield Y.S (0.2% offset) strength
Test conditions Temperature: 25 °c.Moisture: 40% Reference standard ASTM B557 The tensile results obtained experimentally are tabulated in table (6) while are plotted in fig. 2.

HB hardness
The result of table (6) can be plotted as showing in figure (2).Aluminium matrix composites are widely employed for high performance applications.In order to get good mechanical properties the die and squeeze pressure in the casting method is required [4].Figure (2) shows the variation of UTS (Ultimate Tensile Strength) and 0.2 Y.S (Yield Stress) with the reinforcement material Al2O3 wt.%.It is clear that, the increasing wt% of Al2O3 resulting in increase in the UTS and YS.But the maximum increasing values were occurred at 0.4 wt.% Al2O3 for both UTS and Y.S i-e 18.1% and 21.68% respectively.The improvements in the above properties may be due to the reasons: 1.The high dislocation density, the high mechanical properties.The high dislocation density is coming from good bounding between the reinforced material and metal matrix [13].2. The less porosity during fabricating the composite resulting in raising the above mechanical properties [15].

Ductility
Fig [3] shows the variation of ductility vs various wt% of Al2O3.It is clear that the ductility of 2024 Al2O3 decrease with increasing the Alumina wt%.All the values of ductility of composite are less than that of as cast Al alloy.The maximam reduction was occoured at 0.4 wt% of reinforced material of 25.71%.But Mazahery et al [5] examined the ductility of 356 Al/Al2O3 nano composites fabricated by stir casting method and they found that the maximum improvement was happened at 2.5 Al2O3 vol% casted at 800C.

Conclusions
The experimental results revealed the following remarks obtained from this study.1.All the mechanical properties (Hardness, U.T.S and 0.2Y.S) were found to be higher than theas cast 2024 Al alloy.

Table 1 , Chemical Composition wt. % of 2024/Al alloy.
Note:The standard values represent maximum if range not shown, Al is balance wt.%.