Plasma spray of biofunctional(Mg, Sr)-substituted hydroxyapatite coatings for titanium alloy implants

Plasma-sprayed hydroxyapatite (HA) coatings have been widely utilized in load-bearing titanium alloy implants. In this study, Mg, Sr co-substituted HA ((Mg,Sr)-HA) nano-scale powders have been synthesized, which are further used to prepare (Mg,Sr)-HA coatings on Ti-6A1-4V alloys in order to improve the biological functions. The average size of (Mg,Sr)-HA nano particles is ~75nm. The average bonding strength for (Mg,Sr)-HA coating and samples after heat treatment at 500℃ or 600℃ for 3h are 26.17±2.11 MPa, 36.07±4.48 MPa and 37.07 ±2.95 MPa, respectively. There is a significantly increase of bonding strength likely due to low residual stress after heated treatment.MC3T3-E1 cells show a high proliferation rate when cultured with (Mg,Sr)-HA coating extract compared to the normal culture medium, which also exhibit large extension and depositi on of extracellular matrices when adhered on the coating surfaces. Thus, these (Mg,Sr)-HA coatings show high bonding strength and improved biological functions, which offer promising future applications in the fields of orthopedics and dentistry.

Dissimilar Al/Mg alloys friction stir lap welding with Zn foil assisted by ultrasonic

The Zn-added ultrasonic assisted friction stir lap welding(UaFSLW) was carried out to improve the quality of dissimilar Al/Mg alloys joint. The effects of ultrasonic power on the joint quality were also investigated.The results indicated that the larger effective lap width and mixing region between Mg and Al(Mg/Al MR) were attained by Zn foil addition and external ultrasonic assistance. Compared with the conventional joint, the finer and better-distributed Mg-Zn IMCs placing the continuous Al-Mg IMCs were formed in the Mg/Al MR of the Zn-added UaFSLW joint. The Zn foil addition and external ultrasonic assistance significantly improved the tensile shear load of the joint, and the load was increased with the increase of the ultrasonic power. The maximum tensile shear load of 7.95 kN was attained, which was 52.6% larger than that of the conventional joint.

Improving Joint Morphologies and Tensile Strength of Al/Mg Dissimilar Alloys Friction Stir Lap Welding by Changing Zn Interlayer Thickness

The pure Zn foils with different thicknesses(0.02, 0.05, 0.1, 0.2 and 0.3 mm) were selected as interlayers to improve the quality of friction stir lap welding joint of 7075-T6 Al and AZ31 B Mg dissimilar alloys. The effects of the interlayer thickness on joint formation, microstructure and tensile strength were analyzed. The results displayed that the maximum length of the boundary between stir zone(SZ) and thermo-mechanically affected zone in lower plate was obtained by the addition of the Zn interlayer with 0.05 mm thickness. The Mg–Zn intermetallic compounds(IMCs) were discontinuously distributed in the SZ, replacing the continuous Al–Mg IMCs. The size of Mg–Zn IMCs increased with the increase in the thickness of the Zn interlayer. The maximum tensile shear strength of 276 N mm-1 was obtained by the addition of 0.05 mm Zn foil, which increased by 45.6% of that of the joint without the Zn foil addition.