| Aluminum matrix composites(henceforth referred to as AMCs)play an important role inmodern manufacturing industry.By optimized design of the structure and reinforcement phase,attractive material properties can be obtained.For example,the boron carbide(B4C)reinforced aluminum composite is a promising material,which possesses advantages of both Al and B4 C,and gets a lot of attention in the research and application fields.Al alloys are widely used as matrix material owing to their low density,low cost and good composability.On the other hand,B4 C is considered as an ideal reinforcement for AMCs,because it possesses not only high hardness,but also some other excellent characteristics,such as low density,high temperature stability and good chemical stability.However,the addition of B4 C particles leads to not only the improvement of performance,but also some defects,such as brittleness,more fracture formation sites.In order to balance the positives and negatives,the mass fraction of ceramic reinforcements in AMCs is usually less than 20%.When exceeding this limitation,the AMCs cannot be used due to the significantly increasing brittleness.In this case,a three-layered composite was designed in our work,consisting of Al-B4 C mixed powders as inner layer and pure Al as outer layers.Such composite combines the advantages of B4 C particle reinforced AMCs and layered material.It is worth noted that the mass fraction of B4 C in the inner layer can reach 40%,and under the support of outer Al layer,it still shows better ductility than the conventional B4 C reinforced AMCs.Moreover,its outer layer of pure Al also improves the weldability,meeting the industrial requirement.Traditional fabrication method for layered composite is mainly limited in powder metallurgy,which is suffering on complex processing metallurgy,which is suffering on complex process and high cost.In this research,a simplified semi-continuous casting method,followed by hot rolling was used to fabricate B4 C reinforced Al matrix composites(BRALCs),which would shorten the preparation process and improve the production efficiency.For now,the effect of reinforcement particle size on the mechanical properties of the layered composites has been seldom investigated.It is of great importance to optimize particle size for the final performance of the layered material.BRALCs,with pure Al and 40 wt.%B4C mixed powders inner,pure Al outer layers,was prepared in this research.The average sizes of B4 C particles were 6.5?m,23?m,36.5?m and 70?m,respectively,and the average size of Al particles was 70?m.Results indicate that expect for 6.5?m BRALCs,with increasing reinforcement particle size,the impact strength and ultimate tensile strength of single size BRALCs increase,while hardness decreases.For 6.5?m BRALCs,it can be found the B4 C particles agglomerated at some areas.In order to realize particle close packing and further eliminate particle agglomeration,Horsfield filling principle was applied in this work.Result shows that Horsfield filling principle can reduce B4 C agglomeration areas in the inner layer,when the particle was added to secondary ball,BRALCs could acquire best performance(High hardness,strength and toughness).For double sizes BRALCs,increasing the mass fraction of larger reinforcement particle or the average reinforcement particle size would lead to decreasing hardness value and increasing impact strength as well as ultimate tensile strength,however,in comparison with single size BRALCs,the decreasing in hardness is slightly.The difference in impact strength and ultimate strength among samples is mainly caused by variation in reinforcement particle interval in different samples and residual stress in the interface between matrix and reinforcement.The hardness value of BRALCs is mainly determined by the reinforcement particle density per unit volume in the matrix.As the reinforcement particle density changed obviously in the single size BRALCs,large hardness difference can be observed among samples(from 22.32 to 40.77HB),whereas for double sizes BRALCs,residual stress leads to the variation in hardness value,however,as it is an insignificantly factor for hardness variation,only slightly changes occur.B4C reinforced 7075 Al alloy matrix layered composites(BR7AALCs)as well as Al-7075 Al alloy-Al layered composites(A7AALCs)were fabricated to study the influence of heat treatment conditions on mechanical properties and reinforcement load transfer ability of BR7 AALCs.With increasing solution time and aging temperature,the hardness value,impact strength and ultimate tensile increase.Prolonging aging time will lead to increasing hardnessand strength,while impact strength slightly increases and soon decreases.The continuous increasing yield strength deviation between BR7 AALCs and A7 AALCs indicates the improved reinforcement load transfer ability. |
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